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1. Radiocalcium absorption was measured in duplicate in 10 subjects by the double-isotope method, with calcium as the oral carrier (2.5 mmol). Analysis of variance gave 95% confidence limits for a single measurement of fractional absorption and maximum absorption rate in a given individual of ±16.5% of administered dose and ±18.2% of dose/h respectively. 2. The size of these within individual variations suggests that alterations in the rate of calcium absorption-5-contribute to the week-to-week stabilization of some other controlled variable, such as plasma concentration of calcium. 3. In six of the subjects, calcium absorption was also measured with calcium loads at concentrations of 0.5, 5.0 and 20 mmol. Significant falls in fractional absorption, maximum absorption rate and mean transfer rate occurred as the load increased, together with a rise in mean transit time. Although between-individual differences at a given load were considerable, given a single-test result with a known carrier load, it is possible to predict quite accurately the results which would be obtained if a different carrier load were to be given.

1. A whole-gut perfusion technique has been used to compare the rates of intestinal absorption of sodium and xenon. 2. The calculated transit-time spectra for sodium and xenon across the gut mucosa do not differ significantly either in mean transit time or, for the first 15 min, in shape. 3. These results support the hypothesis that the rate of transfer of sodium from the small intestinal lumen to plasma is limited by blood flow. 4. It is suggested that some features of cholera can be explained by this hypothesis.

1. A new method for measurement of skeletal blood flow is described which depends on the complete extraction of 18F in a single passage through bone. 2. Plasma concentration and urinary excretion are measured over a 2 h period. The technique of impulse analysis is used to determine the initial transfer rate of 18F to bone and extravascular extracellular fluid (ECF). The ECF component is evaluated by using a second tracer (51Cr-EDTA or 82Br) and the bone transfer rate obtained by difference. The 51Cr-EDTA data also provide an estimate of glomerular filtration rate and enable a correction to be applied for urinary bladder retention when necessary. 3. Duplicate measurements of skeletal blood flow in eight normal male volunteers gave mean flows between 4·4 and 5·9% of blood volume/min, or about 4 ml min−1 100 g−1 of bone. The variation between normal subjects was least when the results were expressed as % of blood volume/min rather than ml/min, ml min−1 kg−1 or ml min−1 1·73 m−2 body surface area. The precision of the technique was estimated to be 16·4%. 4. Addition of 1·5% random noise to the input data resulted in an uncertainty of 8·5% in the measurement of skeletal blood flow, suggesting that improved precision depends on closer control of physiological variables. 5. In six patients with severe untreated Paget's disease of bone, skeletal blood flow was 8·4–15·3% of blood volume/min. The increase was significant in all cases. 6. The absorbed radiation dose is low, so that the measurement can be repeated.

1. We have measured the total plasma clearance, renal clearance and equilibrium distribution volume of [14C]oxalate, and the urinary oxalate excretion rate and plasma oxalate levels at approximately 6 month intervals for up to 2.5 years in five patients with primary hyperoxaluria. The renal clearance and distribution volumes of [99mTc]DTPA (diethylenetriaminepenta-acetate) were measured simultaneously to provide estimates of glomerular filtration rate (GFR) and extracellular fluid volume (ECF). The same measurements were made on each of five normal volunteers. 2. Clearances and distribution volumes were measured with a modified single injection technique. 3. The oxalate clearance was two to three times the simultaneously measured GFR in the patients and control subjects. The renal clearance of oxalate was less than the total plasma clearance in the patients. The oxalate distribution volume was approximately 1.5 times the ECF in both the patients and controls. Only small changes were observed over a 2.5 years period in these particular patients. 4. The plasma oxalate concentration was derived from the urinary oxalate excretion rate and the plasma [14C]oxalate clearance. It was raised in the patients. The oxalate removal rate was derived from the total plasma clearance and the plasma oxalate concentration.

1. We have measured the plasma oxalate concentration (POx), urinary oxalate excretion (UOx), oxalate equilibrium distribution volume (ODV), oxalate metabolic pool size [(ODV) × (POx)], total plasma oxalate clearance (PCOx), renal (or dialyser) oxalate clearance (RCOx), non-renal oxalate clearance (NRCOx) and the tissue oxalate accretion rate (TOA)= [(NRCOx) × (POx)] in three patients with severe renal failure due to primary hyperoxaluria who were being treated by peritoneal dialysis or haemodialysis, or by renal transplantation. The clearance (either GFR or dialyser) of [99mTc]diethylenetriaminepenta-acetate (DTPA) and the extracellular fluid volume (ECF) measured as [99mTc]DTPA distribution volume were also determined. 2. Negligible amounts of 14C were found in faeces or as 14CO2 in expired air and hence (NRCOx) = (PCOx-RCOx). 3. Haemodialysis removed oxalate more efficiently than peritoneal dialysis in the patient where a direct comparison was possible. Neither treatment could keep up with the TOA when performed for clinically acceptable times. 4. The plasma oxalate concentrations calculated from 14C clearance through the dialyser and the chemically determined concentration of the oxalate in the dialysate were in the range 111–146 μmol/l. This is higher than in normals and in hyperoxaluric patients who are not in renal failure. Hence, although the ODV and ECF are similar to those of hyperoxaluric patients without renal failure and normal control subjects, the oxalate metabolic pool (ODV × POx) is grossly enlarged. 5. In the patient treated by renal transplantation, the oxalate pool size diminished concurrently with the resumption of oxalate excretion but expanded again as renal function decreased due to oxalosis. 6. The quantitative data show that dialysis procedures can only be a temporary holding operation and the prognosis with transplantation remains bad unless excessive oxalate production can be controlled.

1. Double-tracer studies have been carried out in order to investigate the validity of a whole-gut perfusion technique for the measurement of gut lumen-to-plasma and plasma-to-gut lumen sodium fluxes in man. 2. The use of two tracers permits differentiation between the unabsorbed orally administered sodium in the stools and the sodium which has been absorbed and resecreted. The latter is by no means negligible and may amount to some 30% of the recovered material. 3. The available data do not permit the calculation of the absolute values of the bidirectional fluxes without the introduction of some assumption concerning the reabsorption of the sodium which crosses from the plasma to the gut lumen. It is assumed here that this sodium is absorbed by the gut to the same extent as the orally administered material. Analysis of the kinetics of sodium transfer from mouth to stool direct and via the blood plasma in normal subjects and patients with diarrhoea provided experimental evidence confirming the correctness of this assumption. 4. In eleven normal volunteers the gut lumen-to-plasma flow of sodium averaged 13.0 mmol min−1, implying that the observed absorption averaging 1.65 mmol min−1 represents a relatively small imbalance between the bidirectional fluxes. Although one patient with post-gastrectomy dumping syndrome had high fluxes and another with malabsorption following gut resection gave low values, it is suggested that changes in the fluxes in the same patient are more significant than isolated observations on individuals. 5. Granted the validity of the primary assumption, a considerably simpler technique may be used for clinical and field studies which is sufficiently accurate for most purposes and employs a single tracer.