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Osteoporosis is a significant global health and economic burden associated with bone fracture, morbidity and mortality. Denosumab, a novel human monoclonal antibody second-line treatment, inhibits osteoclast-mediated bone resorption and increases bone mineral density (BMD). Treatment achieves reductions in vertebral, non-vertebral and hip fracture risk. We undertook a service evaluation to review clinical outcomes of patients treated with denosumab in an osteoporosis department that provides regional services. We identified 529 patients (95% female; mean age 72.8 years; 35-98 years), who had at least one dose of denosumab administered for the treatment of osteoporosis. The mean number of denosumab doses administered was 4.9 (range: 1 to 12). 330/529 patients had completed a baseline and post-treatment bone densitometry scan (DXA). The mean observed BMD change at around 18 months at the lumbar spine was +8.4% and at the hip was +3.5%. While the majority have transitioned to shared care administration of treatment within primary care (53%), 20% continue to attend hospital clinics to receive treatment. During follow-up, there were 66 deaths (12%). 15% switched to an alternative treatment or were discharged. This retrospective cohort study demonstrates the clinical effectiveness of denosumab in improving bone mineral density in a real life setting in an ageing, co-morbid population. There has been recent progress with adoption of shared care administration in primary care. As part of a quality improvement programme we have recently developed a dedicated denosumab database and day-case treatment clinic for those receiving treatment in secondary care., Competing Interests: Provenance: externally peer reviewed., (Copyright © 2019 Ulster Medical Society.)

In this Letter, the PANGAEA repository was referred to incorrectly in the 'Code availability' and 'Data availability' sections of Methods: the link should be https://doi.org/10.1594/PANGAEA.893761 instead of https://doi.org/10.1594/PANGAEA.877266 . In addition, the sentence, "However, the more commonly used system 2 (75 kg ha -1  yr -1 ) generates roughly the same benefits as system 1…" should read, "However, the more commonly used system 2 (75 kg ha -1  yr -1 ) generates roughly the same benefits as sugarcane ethanol…" These errors have been corrected in the online versions of the Letter.

Land-use changes are critical for climate policy because native vegetation and soils store abundant carbon and their losses from agricultural expansion, together with emissions from agricultural production, contribute about 20 to 25 per cent of greenhouse gas emissions 1,2 . Most climate strategies require maintaining or increasing land-based carbon 3 while meeting food demands, which are expected to grow by more than 50 per cent by 2050 1,2,4 . A finite global land area implies that fulfilling these strategies requires increasing global land-use efficiency of both storing carbon and producing food. Yet measuring the efficiency of land-use changes from the perspective of greenhouse gas emissions is challenging, particularly when land outputs change, for example, from one food to another or from food to carbon storage in forests. Intuitively, if a hectare of land produces maize well and forest poorly, maize should be the more efficient use of land, and vice versa. However, quantifying this difference and the yields at which the balance changes requires a common metric that factors in different outputs, emissions from different agricultural inputs (such as fertilizer) and the different productive potentials of land due to physical factors such as rainfall or soils. Here we propose a carbon benefits index that measures how changes in the output types, output quantities and production processes of a hectare of land contribute to the global capacity to store carbon and to reduce total greenhouse gas emissions. This index does not evaluate biodiversity or other ecosystem values, which must be analysed separately. We apply the index to a range of land-use and consumption choices relevant to climate policy, such as reforesting pastures, biofuel production and diet changes. We find that these choices can have much greater implications for the climate than previously understood because standard methods for evaluating the effects of land use 4-11 on greenhouse gas emissions systematically underestimate the opportunity of land to store carbon if it is not used for agriculture.

This comment raises concerns regarding the way in which a new European directive, aimed at reaching higher renewable energy targets, treats wood harvested directly for bioenergy use as a carbon-free fuel. The result could consume quantities of wood equal to all Europe's wood harvests, greatly increase carbon in the air for decades, and set a dangerous global example.

Background: Corticosteroid treatment is considered the 'gold standard' for Duchenne muscular dystrophy (DMD); however, it is also known to induce osteoporosis and thus increase the risk of vertebral fragility fractures. Good practice in the care of those with DMD requires prevention of these adverse effects. Treatments to increase bone mineral density include bisphosphonates and vitamin D and calcium supplements, and in adolescents with pubertal delay, testosterone. Bone health management is an important part of lifelong care for patients with DMD., Objectives: To assess the effects of interventions to prevent or treat osteoporosis in children and adults with DMD taking long-term corticosteroids; to assess the effects of these interventions on the frequency of vertebral fragility fractures and long-bone fractures, and on quality of life; and to assess adverse events., Search Methods: On 12 September 2016, we searched the Cochrane Neuromuscular Specialised Register, CENTRAL, MEDLINE, Embase, and CINAHL Plus to identify potentially eligible trials. We also searched the Web of Science ISI Proceedings (2001 to September 2016) and three clinical trials registries to identify unpublished studies and ongoing trials. We contacted correspondence authors of the included studies in the review to obtain information on unpublished studies or work in progress., Selection Criteria: We considered for inclusion in the review randomised controlled trials (RCTs) and quasi-RCTs involving any bone health intervention for corticosteroid-induced osteoporosis and fragility fractures in children, adolescents, and adults with a confirmed diagnosis of DMD. The interventions might have included oral and intravenous bisphosphonates, vitamin D supplements, calcium supplements, dietary calcium, testosterone, and weight-bearing activity., Data Collection and Analysis: Two review authors independently assessed reports and selected potential studies for inclusion, following standard Cochrane methodology. We contacted study authors to obtain further information for clarification on published work, unpublished studies, and work in progress., Main Results: We identified 18 potential studies, of which two, currently reported only as abstracts, met the inclusion criteria for this review. Too little information was available for us to present full results or adequately assess risk of bias. The participants were children aged five to 15 years with DMD, ambulant and non-ambulant. The interventions were risedronate versus no treatment in one trial (13 participants) and whole-body vibration versus a placebo device in the second (21 participants). Both studies reported improved bone mineral density with the active treatments, with no improvement in the control groups, but the abstracts did not compare treatment and control conditions. All children tolerated whole-body vibration treatment. No study provided information on adverse events. Two studies are ongoing: one investigating whole-body vibration, the other investigating zoledronic acid., Authors' Conclusions: We know of no high-quality evidence from RCTs to guide use of treatments to prevent or treat corticosteroid-induced osteoporosis and reduce the risk of fragility fractures in children and adults with DMD; only limited results from two trials reported in abstracts were available. We await formal trial reports. Findings from two ongoing relevant studies and two trials, for which only abstracts are available, will be important in future updates of this review.

Introduction: Osteoporosis results in significant morbidity and mortality for a large number of patients within Northern Ireland. Recombinant PTH (Teriparatide) is one of a growing number of treatment options for the disease., Methods: A retrospective analysis was carried out for all patients who had been commenced on Teriparatide since it was first used in the Belfast Health and Social Care Trust (BHSCT) in 2007. Patient demographics, clinical history and prior treatment were recorded prior to an eighteen month treatment protocol. Outcome measures including bone densitometry, bone turnover markers and health status were assessed on commencement and completion., Results: 138 patients have commenced teriparatide therapy since 2007 (9 male, 129 female). At the time of analysis 60 patients had completed treatment, 53 patients were receiving ongoing treatment and 25 patients did not complete the 18 month course. On completion vertebral bone mineral density (BMD) had increased by 8.3% while femoral neck BMD had increased by 3.5%. Bone turnover markers demonstrated a significant increase of bone formation and resorption at 4 months, with a smaller increase at 18 months. Health outcome measures (EuroQoL-5 and patient visual analogue scale) indicated improvement in the quality of life of patients of those who completed the treatment course., Conclusions: Experience in the BHSCT with teriparatide since 2007 demonstrates improvement in BMD comparable to published data, changes in bone turnover markers consistent with increased bone remodeling and better health outcomes for patients.

Background: The aims of this study were to review and update previous projections of the number of proximal femoral fractures in the Northern Ireland population and to ascertain if the trend of increasing age-specific fracture incidence was continuing., Methods: Data from 1985 to 1997 was obtained from hospital theatre records to ascertain the number of surgical procedures for proximal femoral fracture. Data for the years 2005 and 2010 was obtained from Northern Ireland's Fracture Outcomes Research Database (FORD) and locally held records in one region not then using FORD. Demographic details were obtained from data published by the Northern Ireland Statistics and Research Agency. Age-specific fracture rates were calculated for males and females in 5 year age brackets and for populations aged 50+ and 65+. Updated projections for the number of proximal femoral fractures by 2020 were made assuming the continuation of the same age-specific fracture rates observed in 2010., Results: From 1997 to 2010 the age-specific fracture incidence has fallen or plateaued across most observed age and sex subgroups. Over the period 2010 to 2020, male and female fracture numbers are projected to increase by 23% and 21% respectively which equates to approximately 400 extra proximal femoral fractures., Conclusion: Over the next decade there will be an increasing burden on Northern Irish healthcare resources attributed to a rise in the number of proximal femoral fractures. The age-specific fracture rates in this population are no longer rising and hence the expected increase in healthcare costs is primarily a consequence of the anticipated changing demographic trends.

We address the quantum Hall behavior in twisted bilayer graphene transferred from the C face of SiC. The measured Hall conductivity exhibits the same plateau values as for a commensurate Bernal bilayer. This implies that the eightfold degeneracy of the zero energy mode is topologically protected despite rotational disorder as recently predicted. In addition, an anomaly appears. The densities at which these plateaus occur show a magnetic field dependent offset. It suggests the existence of a pool of localized states at low energy, which do not count towards the degeneracy of the lowest band Landau levels. These states originate from an inhomogeneous spatial variation of the interlayer coupling.

Bio-energy, that is, energy produced from organic non-fossil material of biological origin, is promoted as a substitute for non-renewable (e.g., fossil) energy to reduce greenhouse gas (GHG) emissions and dependency on energy imports. At present, global bio-energy use amounts to approximately 50 EJ/yr, about 10% of humanity's primary energy supply. We here review recent literature on the amount of bio-energy that could be supplied globally in 2050, given current expectations on technology, food demand and environmental targets ('technical potential'). Recent studies span a large range of global bio-energy potentials from ≈30 to over 1000 EJ/yr. In our opinion, the high end of the range is implausible because of (1) overestimation of the area available for bio-energy crops due to insufficient consideration of constraints (e.g., area for food, feed or nature conservation) and (2) too high yield expectations resulting from extrapolation of plot-based studies to large, less productive areas. According to this review, the global technical primary bio-energy potential in 2050 is in the range of 160-270 EJ/yr if sustainability criteria are considered. The potential of bio-energy crops is at the lower end of previously published ranges, while residues from food production and forestry could provide significant amounts of energy based on an integrated optimization ('cascade utilization') of biomass flows.

We report a case of paraneoplastic limbic encephalitis (PLE) in an elderly lady with small-cell lung carcinoma (SCLC) and positive anti-RI neuronal auto-antibody. PLE is a relatively rare clinical entity associated with cancer patients, but is probably under-diagnosed. PLE typically presents clinically with affective changes in personality, cognitive dysfunction and seizures in a patient with malignancy, particularly SCLC. Although diagnosis does not rely upon definitive investigation results, serum paraneoplastic antibodies, abnormal CSF, and characteristic MRI and EEG findings may support the diagnosis. As PLE often presents prior to the discovery of a primary tumour, knowledge of the disease may assist in identifying underlying malignancy.

Osteoporosis, although considered less common, still occurs in men. We present a cross-sectional study of a group of Northern Ireland men with low-trauma forearm fractures to determine the presence of osteoporosis and screen for secondary causes of low bone mineral density. Male patients aged 30-75 years, presenting with distal forearm fracture in 2000-2001 in Northern Ireland, were identified through a Colles fracture database. A total of 37 subjects consented to have bone mineral density measurements undertaken at the femoral neck, spine and forearm using a Lunar expert bone densitometer. Twenty-seven percent of the men had osteoporosis at the spine, femoral neck or forearm, as defined by a bone mineral density score of less than -2.5. We also found that 49% of patients had vitamin D insufficiency or deficiency, 27% had low serum testosterone, 14% had abnormal liver function test results, and 14% had raised parathyroid hormone. Only one patient received advice or treatment regarding osteoporosis at the time of fracture. Increased awareness of male osteoporosis and the need for screening for potential secondary causes in this group of patients is required, both at primary and secondary care level.

Background: Many studies have investigated the prevalence of 25-hydroxy-vitamin D inadequacy throughout the world and found a high prevalence of 25-hydroxy-vitamin D inadequacy in older patients, particularly those with fragility fracture., Scope: To review the findings from vitamin D audits from six units across the UK and compare with previously published data from around the world. Results from four units have been previously published (Belfast, Glasgow, London and Medway) and this paper presents new data from Southampton and Carshalton, and further sub-analysis of the data from Medway., Findings: Three audits of patients attending metabolic bone clinics (Carshalton, Medway and Southampton) identified 954 patients, of which overall 49% had a prior fragility fracture. Mean 25-hydroxy-vitamin D levels ranged from 47.7 nmol/L to 62.4 nmol/L. Of these patients 72.9-88.9% had a 25-hydroxy-vitamin D level < 80 nmol/L, 68.8-83.3% < 70 nmol/L and 37.5-59.1% < 50 nmol/L. The mean age of patients ranged from 60.0 to 67.5 years. Sub-analysis of the data by fracture status revealed that patients with fracture had lower mean levels of 25-hydroxy-vitamin D compared with patients without fracture. This was statistically significant in the sub-analysis of the Medway data (45.3 nmol/L versus 49.9 nmol/L, p < 0.005). Three audits identified 330 patients with fragility fracture. Audits from Glasgow and Belfast specifically identified patients with fragility fracture. A subgroup of patients with fracture aged over 50 years from the Medway audit was also included in this group. Mean levels of 25-hydroxy-vitamin D ranged from 40.0 nmol/L to 52.3 nmol/L. 83.7-96.4% of patients had a 25-hydroxy-vitamin D level < 80 nmol/L, 73.3-89.7% < 70 nmol/L and 55.8-73.2% < 50 nmol/L. The mean age of patients ranged from 65.3 to 68.6 years. The audits carried out in Belfast and Medway were also divided by supplementation status. Mean 25-hydroxy-vitamin D levels were 48.1 nmol/L in Belfast and 40.5 nmol/L in Medway in the patients not receiving supplements and 53.8 nmol/L and 59.9 nmol/L, respectively in the patients receiving supplements. The difference was statistically significant in the Medway audit (p < 0.0001), but not in the smaller Belfast audit (p = 0.216). As would be expected, the prevalence of 25-hydroxy-vitamin D inadequacy was higher in the patients not receiving supplements, for example at the 70 nmol/L threshold: 82.6% versus 67.1% in Belfast and 89.6% versus 72.7% in Medway. Three audits specifically identified 694 patients with hip fracture (Belfast, Glasgow and London). Mean levels of 25-hydroxy-vitamin D ranged from 24.7 nmol/L to 36.1 nmol/L. Of these patients 90.7-99.0% had a 25-hydroxy-vitamin D level < 80 nmol/L, 88.4-98.0% < 70 nmol/L and 81.6-92.7% < 50 nmol/L. The mean age of patients ranged from 73.4 to 80.5 years., Conclusion: Inadequate 25-hydroxy-vitamin D levels are extremely common in the elderly and particularly so in patients with fragility fracture - specifically in those with hip fracture. Although the differing audit specifications and assay techniques used make direct comparisons difficult, the data do provide a snapshot of 25-hydroxy-vitamin D status across the UK and are consistent with those previously observed elsewhere in Europe and the rest of the world.

Background: It is well established that vitamin D levels are sub-optimal in older people and that adults with fragility fracture have low levels of serum vitamin D., Objectives: To investigate the prevalence of vitamin D inadequacy in an elderly population with fragility fractures and to compare data with previously published work from Glasgow., Research Design and Methods: Two retrospective patient audits were carried out using records from the out-patient Osteoporosis Clinic at Musgrave Park Hospital and from in-patient hip fracture admissions at the Royal Victoria Hospital., Results: There were data for 86 patients with fragility fracture from the Osteoporosis Clinic, 40.7% patients had vertebral fractures and 10.5% multiple fractures. Patients with hip fracture were excluded from the analysis. 69.8% of the patients were women. The mean age at the time of fracture was 65.3 years and 70.9% of patients were aged 60 years or over and 32.6% were aged 75 years or over. At the time of out-patient attendance, 73.3% were receiving supplementation with calcium and vitamin D. The mean vitamin D level was 52.3 nmol/L (21.0 ng/mL), SD = 23.4 (9.4). There were 83.7% of patients who had a vitamin D level < 80 nmol/L, 73.3% < 70 nmol/L and 55.8% < 50 nmol/L. There were no significant differences by patient age or sex. Data were also analysed according to supplementation status, in patients not taking supplements (n = 23) mean vitamin D level was 48.1 nmol/L (19.3 ng/mL), SD = 27.4 (11.0) compared with 53.8 nmol/L (21.6 ng/mL), SD = 21.8 (8.7) in the 63 patients taking supplements. Prevalence of inadequacy was higher in the patients not taking supplements 82.6% versus 67.1% at the 70 nmol/L threshold. There were data for 43 hip fracture patients, 95.3% of the patients were women. The mean age at the time of fracture was 78.3 years, 95.3% of patients were aged 60 years or over and 69.8% were aged 75 years or over. Data were not available on whether these patients were receiving supplementation. The mean vitamin D level was 36.1 nmol/L (14.5 ng/mL), SD = 24.8 (9.9). 90.7% of patients had a vitamin D level < 80 nmol/L, 88.4% < 70 nmol/L ( approximately 28 ng/mL) and 88.4% < 50 nmol/L ( approximately 20 ng/mL)., Conclusions: The levels of vitamin D inadequacy revealed in this audit were similar to those in an earlier audit carried out in Glasgow. Thus studies at two locations in the UK confirm the high prevalence of vitamin D inadequacy, furthermore, the prevalence of inadequacy appears to be higher in those patients with a hip fracture.

How are we to cope with the complex problems that now surround elderly patients with fractures? What are these problems and what systems should be in place to address them? No matter how successful we may be in treatment of osteoporosis and prevention of falls, it is inevitable that a massive worldwide increase in incidence of fragility fractures will occur in the next 50 years. It is crucial that we upgrade our systems to cope with this, if severe disruption of health services is to be avoided. This review considers the topics of falls, osteoporosis, and impact modification. We review the major medical issues that should be addressed in delivering hospital care that is efficient and of high quality. Various models for organizing the necessary liaison between fracture staff and medical or geriatric staff are examined and the current literature regarding orthogeriatric care is reviewed. We propose that the model of continuous orthogeriatric care, as practiced in Belfast, may be the way forward in addressing the complex problems associated with elderly patients with fractures. A system of ongoing audit of treatment outcomes and the journey of care for elderly patients with fractures of the proximal femur is necessary as a monitoring tool in developing the optimal system for orthogeriatric liaison.

Background and Objectives: The aim of this study was to evaluate the prognosis after treatment for femoral neck fracture, to assess the impact of delay to surgery, and to devise a clinical prediction rule and score., Methods: A prospective observational study was conducted in which 1780 patients treated surgically in two teaching hospitals between 1 November 1997 and 31 October 1999 were followed over 12 months. Logistic regression was used to distinguish the effects of predictor variables on survival. Using a probit transformation of the predicted posterior probabilities of death, a prognostic score was devised with scores constrained so that a nominal score of approximately 90 represented a 50:50 chance of survival over 12 months., Results: Mortality was 30.1% in men and 19.5% in women. Increasing age, male gender, longer pre-operative delay, a higher American Society of Anesthesiology score, a lower Mental Test score, and a lower activities of daily living (Barthel) score were associated with increased risks of death. Of those waiting between 1 and 5 days for surgery, approximately 8 medium-risk and 17 high-risk patients (with prognostic scores of 90 and 120, respectively) would have to have their delay reduced to < 24 hours to yield one additional survivor., Conclusion: The application of prediction rules must be guided by ethical, social, and scientific concerns.

Plasma concentrations of atrial natriuretic peptide immunoreactivity (irANP) and brain natriuretic peptide immunoreactivity (irBNP) in elderly normal subjects (mean age 71.1, range 66-81 years, n = 10) were examined before (rest), during (peak of exercise) and after (3 min, 6 min) a treadmill exercise test (modified Bruce protocol). An attempt was also made to determine the effect of steady state exercise (30% and 50%) and posture (supine, sitting) on circulating levels of atrial natriuretic peptide and calcitonin gene-related peptide (CGRP) in man. The results suggest that exercise gives rise to increased levels of irANP and irCGRP, but not human BNP. The study also demonstrated a >40% rise in irCGRP and irANP levels at 50% steady state exercise compared with 30% steady state exercise. irCGRP was shown to decline in the upright position compared with the supine position, and irCGRP did not rise with exercise. Although ANP is normally stored in large concentration in the atria with much less in the ventricles and BNP is derived to a much greater extent from the ventricles, the differential release rate of these peptides may make BNP concentration a more sensitive indicator of left ventricular dysfunction than ANP. The observations obtained here also raise the possibility that the ANP system may not only help to eliminate intermittent overhydration, but also participate in the postural regulation of diuresis and natriuresis and perhaps even support the maintenance of excretory kidney function in the ageing subjects.

The rate of polarized secretion of a putative adhesion ligand, sialosyl Lewis(a) (19-9), by SW1116 colorectal carcinoma cells is stimulated at least 20-fold after pre-incubation with, and the incorporation of, retinoic acid (RA). In order to investigate the possible involvement of fatty acylation in the export of the epitope, purified ligands from carcinoma-cell membranes, membrane subfractions and media were analyzed during RA-induced secretion. Incorporation of radioactivity from (3H)palmitate into membrane subfractions and purified sialosyl Lewis(a) antigenic molecular species of M(r) > 150,000 (SiaLeams) was stimulated by RA treatment. Most of the intracellular lipid radioactivity which bound to solid-phase 19-9 antibody behaved chromatographically, either like ganglioside or like NH2 OH-labile acyl groups, but most of the (3H) bound to SiaLeams of post-incubation media behaved like base-labile fatty acyl groups, or free fatty acid. Release of base-labile lipid radioactivity after 3 hr (associated with antigen) was almost exclusively into the apical media of membrane inserts. Gas-liquid chromatography/mass spec. analyses of purified Sialeams revealed the presence of palmitate (16:0), as well as stearate (18:0) and oleate (18:1) fatty acyl groups. Our results suggest that fatty acylation of SiaLeams may be co-ordinated with alterations in glycosylation and participate in directing these molecules to the apical surface. Lipid analyses were consistent with ganglioside chaperonage of SiaLeams to the apical surface, where N-fatty-acylated gangliosides remain for the most part integrated into the bilayer, but some oxyester or thioester bonds may be cleaved to permit release of SiaLeams to the apical medium.

In the course of prenatal care, the sera from 5670 pregnant women were investigated. The average infection rate in the population was 39.22%; 60.39% were seronegative. To minimise the risk involved in toxoplasmosis infection, toxoplasma-antibodies must be definitely determined during prenatal care. This should be carried out simultaneously with the determination of antibodies to the rubella virus.

Two cases of primary hypothyroidism with hypopituitarism in elderly patients are reported. The elevated levels of thyroid stimulating hormone led to delay in the recognition of accompanying pituitary failure. Elderly patients should not be commenced on thyroxine replacement therapy until the possibility of hypopituitarism and cortisol deficiency has been excluded.

In flow-pressure studies of the perfused "forebody', newborn (3-12 h old) SHR demonstrated significantly lower pressures than newborn WKY at high flow rates. Newborns from dams fed high salt during pregnancy showed no significant differences in flow-pressure relationships from newborns of the corresponding strain whose dams received standard salt. At 2 weeks, SHR continued on standard salt had pressures not significantly different from those of WKY at intermediate and high flow rates. However, 2-week standard salt SHR did demonstrate significantly lower pressures at low perfusion rates than 2-week WKY. 2-week SHR on high salt showed strikingly lower pressures at high flows than 2-week standard salt SHR.

Media/lumen area ratios and density of arteries and arterioles were obtained from tail sections of newborn and 2-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) on prenatal/postnatal high salt diets or standard salt diets. Fixation was by a solution which caused minimal contraction and no differences in contractile response between SHR and WKY. Standard salt SHR of both ages demonstrated significantly greater media/lumen ratios in intermediate size arterioles but not in smaller or larger arterial categories. Prenatal high salt caused significant medial thickening in 49- to 58- micrometer arterioles of newborn SHR. Maintenance on high salt to 2 weeks caused significant medial thickening i SHR arterioles of 19-38 micrometer outside diameter. High salt significantly increased the density of terminal arterioles in 2-week SHR.

Sarcoplasmic reticulum (SR) of fast extensor digitorum longus (EDL) and slow soleus (SOL) muscles of the mouse was examined by freeze-fracture techniques. A distinctive feature of sarcoplasmic reticulum from the EDL is the presence of hillocks on the A-face within the terminal cisterns. These hillocks are usually arranged in a single row which is deployed parallel to the long axis of the adjacent T-tubule. Center-to-center spacing of hillocks within a row is about 70-75 nm. Hillocks are also found scattered within the collar region. The EDL of ten week mice was characterized by sheet-like terminal and intermediate cisterns, the latter being replaced in 37 week animals by thin tubular longitudinal elements of the SR which contain no hillocks or dimples. Hillocks occur only occasionally in SR from 10 or 20 week SOL muscle. In such cases the hillocks occur singly rather than in rows as in the terminal cisterns of EDL. The predominant form of SR in the SOL contains no hillocks. Total particles in the A-face of EDL-SR (2996 particles/mu2; S.D. = +/- 287) slightly exceeded that of SOL-SR (2558 particles/mu2; S.D. = 274 8 NM). Packing density of 8 nm particles was slightly higher for EDL (750/mu2) VS. SOL (700/mu2). The possible significance of these features of SR in fast and slow muscle is discussed.