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Fuel sloshing-induced damping is currently being studied extensively within the EU-funded SLOWD project as a means of passively reducing dynamic loads in aircraft wings. It is of interest to be able to determine which parameters have the greatest influence on the added damping from the sloshing motion. An uncertainty in the measured sloshing force has been observed when multiple consecutive and identical oscillation cycles are considered in sinusoidal excitation experiments, leading to variations in the measured energy dissipation. This current work considers liquid undergoing vertical sloshing motions for different fill level and excitation conditions (frequency and amplitude) leading to energy dissipation via several possible physical mechanisms. The sloshing dissipation is measured experimentally across a large number of excitation cycles and for each excitation amplitude, expressed in the form of Froude (Fr) numbers. Depending on the Fr number, distinct sloshing mechanisms dominate the dissipative effects and induce a particular variance across the identical cycles analysed. The sloshing-induced energy dissipation variation is quantified and correlated with different mechanisms depending on Fr number, helping to explain various non-stationary effects that are observed even in well-controlled experimental conditions. As well as improving the insights into the inherent dispersion nature of the studied phenomena, this research also establishes experimental characteristics suitable for future model validation and calibration.

In this paper, a variable structure control strategy is adopted to improve position accuracy of Diamond 600k, a 2-Dof parallel manipulator. Firstly, mechanism and servomotor dynamics are developed in terms of the virtual work principle, while the mechantronics coupling model of the manipulator is formulated according to the equivalent torque. At this stage, the mass matrix of the mechanism is calculated individually to decouple the systematic model. This can effectively reduce the computational burden of the dynamic model in the real time control process. Then, various path-planning methods are compared with each other in order to explore which of them is more suitable to the high-speed manipulator. Last, results of the relevant experiments and simulations are presented from which it is easily can be seen that in comparison to conventional PID controller, the algorithm developed in this paper provides more reliable tracking performance.

Depleted soil nitrogen supplies in long-term continuously cultivated soil for cereal grain cropping have resulted in reduced cereal yields, low grain proteins and hence low economic returns. This has necessitated the development of alternative management practices to sustain crop yields, as well as to restore and maintain soil fertility. In the present study we examined the comparative performance of several management options over a 12-year period, including: a 4-year rotation of grass + legume pasture followed by wheat (GL–wheat); 2-year rotations of lucerne–wheat, annual medic–wheat and chickpea–wheat; and continuous conventional tillage (CT) or no-tillage (NT), without or with fertiliser N application (0, 25 and 75 kg N ha–1 for each crop). Average wheat grain yields were highest in the chickpea–wheat rotation, followed by the NT wheat with 75 kg N ha–1; the lowest grain yields were in the CT or NT wheat treatment without fertiliser N application. Crop water use and gross margin were strongly correlated. However, there was an increasing potential for the deep leaching of nitrate-N at 75 kg N ha–1 application, as well as from the GL pasture initiated in 1987, but not from that initiated in 1986, emphasising the effect of variability in growing seasons. Soil organic C stocks increased under the 4-year GL pasture in the 0–0.1 m depth only, then decreased steadily following the cropping phase. The rotation of 4-year GL pasture followed by wheat cropping for 4–6 years may maintain initial soil organic C stock, but a shorter cropping phase is required to increase soil organic C and N stocks and soil fertility in the long term. Partial economic analysis of the treatments suggested that restoring or maintaining soil N fertility, either through legume-based pastures, grain legume and/or N fertiliser, provides long-term positive economic return.

BackgroundThere are no published reports of cross-cultural equivalence and interrater reliability at the level of individual symptom items assessed by a semi-structured clinical interview employing operationalised clinician ratings.AimsTo assess the cross-cultural clinical equivalence and reliability of a Chinese version of the World Health Organization Schedules for Clinical Assessment in Neuropsychiatry (SCAN).MethodUK-US and Taiwanese groups of psychiatrists used Chinese and English transcripts of videotape interviews of Taiwanese patients to discuss cross-cultural issues and ratings of SCAN items. Item ratings were compared quantitatively individually and pooled by SCAN section.ResultsChinese equivalents were found for all SCAN items. No between-group differences were found for most individual items, but there were differences for some scaled items. Average agreement between the two groups was 69–100%.ConclusionsCross-cultural implementation based on SCAN in Taiwan appears valid.

The fate of 14C-naringenin during its specific activation of nod genes in Rhizobium leguminosarum bv. viciae was examined. After incubation with either strain RBL5560 or its pSym-cured derivative in a medium supplemented with 14 C-naringenin at nod gene-inducing concentrations of 2 nM (ca. 12.5 kBq) plus cold acetate (0.5 μM), a radiocarbon inventory for the cells and supernatant extracts was obtained. The level of 14 C-label incorporation was also determined in the fractionated cellular components. Using 14 C-acetate at 0.5 μM (1036 kBq) and cold naringenin (2 nM) in incubations with strain RBL5560 as a separate treatment, the Nod metabolites were detected by thin layer and high performance liquid chromatographic methods and the data provided the basis for identification of the Nod factors from the supernatant obtained from 14 C-naringenin treatments. Subsequent radio-biochemical and chemical analyses revealed that RBL5560 cells assimilated 14 C-naringenin during the activation of nod genes. Our analysis also showed that labelled carbon atoms from the 14 C-naringenin were incorporated into the acyl moiety of a lipo-oligosaccharide Nod factor, NodRlv IV, present in the culture supernatants of RBL5560. The pSym-cured derivative failed to synthesize any Nod metabolites in a 14 C-naringenin supplemented medium. The tracing of flavonoid-derived carbon atoms to the acyl chain of a host-specific Nod factor, a moiety that defines host specificity for this Rhizobium, adds a new dimension to the signalling function of flavonoids in legume-Rhizobium interactions.

A combined subtraction hybridization and polymerase chain reaction/amplification technique was used to develop a DNA probe which was specific for the Rhizobium leguminosarum biovar phaseoli and the Rhizobium tropici group. Total genomic DNA preparations from Rhizobium leguminosarum biovar viciae, Rhizobium leguminosarum biovar trifolii, Rhizobium sp., Agrobacterium tumefaciens, Rhizobium fredii, Bradyrhizobium japonicum, Bradyrhizobium ssp. and Rhizobium meliloti were pooled and used as subtracter DNA against total genomic DNA from the Rhizobium leguminosarum biovar phaseolo strain KIM5s. Only one round of subtraction hybridization at 65°C was necessary to remove all cross-hybridizing sequences. Dot blot hybridizations with total genomic DNA of the eight subtracter organisms and 29 bacteria of different groups confirmed the high specificity of the isolated DNA sequences. Dot blot hybridizations and total genomic DNA from ten different R. Leguminosarum biovar phaseoli and R. tropici strains resulted in strong hybridization signals for all strains tested. The DNA probe for the R. tropici and R. leguminosarum biovar phaseoli group was used for dot blot hybridization with DNA extracts from three tropical and one boreal soil. When correlated with data from Most Probable Number analyses the probe was capable of detecting as low as 3 × 104 homologous indigenous rhizobia per g soil. The technique offers great benefits for the development of DNA probes for monitoring bacterial populations in environmental samples.

Since the first volume of Bergey's Manual of Systematic Bacteriology was published, in 1984, two additional genera and several new species of stem- and root-nodulating bacteria have been proposed; further changes to the taxonomy of this group of organisms appear likely. This paper briefly reviews the current status of “Rhizobium” taxonomy and proposes minimal standards for the description of future genera and species belonging to this group of organisms.

Release of soluble reactive phosphorus (SRP) from dissolved organic phosphorus (DOP), concentrated by reverse osmosis of water samples from Lough Neagh Northern Ireland, was measured in the presence of enzymes and cultures of lake water bacteria in a basal liquid medium adjusted to the pH of lake water (7.6). No hydrolysis of unfractionated DOP was observed in the presence of alkaline phosphatase but a combination of alkaline phosphatase and phosphodiesterase mineralized 14% of DOP in a 30 day incubation period at 15 °C. A similar amount of mineralization was attained by phytase. Phytase induced the same degree of mineralization in a range of DOP fractions varying from MW > 100 000 to c. 500. A mixed culture of lake water bacteria mineralized 12% of unfractionated DOP. Single cultures of lake water bacteria displayed low mineralizing activity (mean of 49 cultures = 5% DOP hydrolysed). Results indicate that DOP from Lough Neagh in the above molecular weight range is predominantly recalcitrant to bacterial mineralization under natural lake conditions.

Clinical and pathologic findings of avian paramyxovirus type 1 (PMV-1) in 19 houbara bustards (Chlamydotis undulata macqueenii) imported from Pakistan into the United Arab Emirates and one captive-bred bird are reported. Clinical signs included circling, walking backward, ataxia, opisthotonos, torticollis, recumbency, head tilt, head shaking, head tremor, tucking of head under keel, nasal discharge, conjunctivitis, and diarrhea. The length of time imported birds exhibited clinical signs varied from 4 days to 18 mo after importation. Hemagglutinating antibodies against PMV-1 were detected in the sera of all 17 birds from which blood samples were collected, and PMV-1 was isolated from pooled brain, spleen, and lung tissues from two birds with acute clinical signs. There were no distinctive gross lesions at necropsy, and histologic findings were consistent with but not pathognomonic for PMV-1. All houbara bustards managed in a captive breeding and restoration program established by the National Avian Research Center have been vaccinated against PMV-1 since October 1992, and no case of PMV-1 has been reported in this collection since that time.

Research was conducted to develop a more accurate and less time-consuming method of determining expressible moisture in poultry meat. Two modifications of wrapping meat in netting (fold wrap or basket wrap) were compared to a conventional method that did not include wrapping meat. Ground, dark poultry meat, with and without 2.0% added NaCl, was wrapped in netting and analyzed for expressible moisture. The fold wrap method was determined to be more accurate and easier to use, as less expressed meat adhered to the surrounding filter papers. Thus, actual expressed moisture absorbed by filter papers was measured.

Gas chromatographic and mass spectrometric analyses of derivatized culture medium extracts were used to identify the products of flavonoid metabolism by rhizobia. A number of Rhizobium species and biovars degraded their nod gene-inducing flavonoids by mechanisms which originated in a cleavage of the C-ring of the molecule and which yielded conserved A- and B-ring products among the metabolites. In contrast, Pseudomonas putida degraded quercetin via an initial fission in its A-ring, and Agrobacterium tumefaciens displayed a nonspecific mode of flavonoid degradation which yielded no conserved A- or B-ring products. When incubated with rhizobia, flavonoids with OH substitutions at the 5 and 7 positions yielded phloroglucinol as the conserved A-ring product, and those with a single OH substitution at the 7 position yielded resorcinol. A wider range of structures was found among the B-ring derivatives, including p-coumaric, p-hydroxybenzoic, protocatechuic, phenylacetic, and caffeic acids. The isoflavonoids genistein and daidzein were also degraded via C-ring fission by Rhizobium fredii and Rhizobium sp. strain NGR234, respectively. Partially characterized aromatic metabolites with potential nod gene-inducing activity were detected among the products of naringenin degradation by Rhizobium leguminosarum bv. viciae. The initial structural modification of nod gene-inducing flavonoids by rhizobia can generate chalcones, whose open C-ring system may have implications for the binding of inducers to the nodD gene product.

The polymerase chain reaction was used to amplify the staphylococcal enterotoxin B and C genes (entB and entC1) and the staphylococcal nuclease gene (nuc). Two sets of primers ("nested primers") were found to be necessary for the detection of low copy numbers of purified DNA in diluent. These allowed detection of ca. 1 fg of purified target DNA, while 100 pg was required before detection of entB, entC1, and nuc with single primer pairs was possible. With nested primers, enterotoxigenic Staphylococcus aureus cells could be detected in artificially contaminated dried skimmed milk samples at levels of ca. 10(5) CFU ml-1 within 8 h. No cross-reaction was observed between the highly homologous entB and entC1 genes. The method showed total specificity for entC1 when tested against a wide variety of other bacteria.

Lotus rhizobia catabolized quercetin in an arabinose-based medium via a novel form of C-ring cleavage, yielding phloroglucinol and protocatechuic acid. Conservation of the A and B rings of the flavone suggests that a chalcone could be formed as a transient intermediate.

Comments are made on the main categories by which specific states of morbid anxiety are classified in the ICD-9, ICD-10, DSM-III and DSM-III-R. The latest classifications, ICD-10 and DSM-III-R, contain many more such categories than ICD-9, and although they differ in the priority given to panic versus agoraphobia, the content is very largely similar. ICD-10 contains several categories of special interest to mental health workers in developing countries and primary health care.

Reduced supplies of nitrogen (N) in many soils of southern Queensland that were cropped exhaustively with cereals over many decades have been the focus of much research to avoid declines in profitability and sustainability of farming systems. A 45-month period of mixed grass (purple pigeon grass, Setaria incrassata Stapf; Rhodes grass, Chloris gayana Kunth.) and legume (lucerne, Medicago sativa L.; annual medics, M. scutellata L. Mill. and M. truncatula Gaertn.) pasture was one of several options that were compared at a fertility-depleted Vertosol at Warra, southern Queensland, to improve grain yields or increase grain protein concentration of subsequent wheat crops. Objectives of the study were to measure the productivity of a mixed grass and legume pasture grown over 45 months (cut and removed over 36 months) and its effects on yield and protein concentrations of the following wheat crops. Pasture production (DM t/ha) and aboveground plant N yield (kg/ha) for grass, legume (including a small amount of weeds) and total components of pasture responded linearly to total rainfall over the duration of each of 3 pastures sown in 1986, 1987 and 1988. Averaged over the 3 pastures, each 100 mm of rainfall resulted in 0.52 t/ha of grass, 0.44 t/ha of legume and 0.97 t/ha of total pasture DM, there being little variation between the 3 pastures. Aboveground plant N yield of the 3 pastures ranged from 17.2 to 20.5 kg/ha per 100 mm rainfall. Aboveground legume N in response to total rainfall was similar (10.6–13.2 kg/ha per 100 mm rainfall) across the 3 pastures in spite of very different populations of legumes and grasses at establishment. Aboveground grass N yield was 5.2–7.0 kg/ha per 100 mm rainfall. In most wheat crops following pasture, wheat yields were similar to that of unfertilised wheat except in 1990 and 1994, when grain yields were significantly higher but similar to that for continuous wheat fertilised with 75 kg N/ha. In contrast, grain protein concentrations of most wheat crops following pasture responded positively, being substantially higher than unfertilised wheat but similar to that of wheat fertilised with 75 kg N/ha. Grain protein averaged over all years of assay was increased by 25–40% compared with that of unfertilised wheat. Stored water supplies after pasture were

Continuous cultivation and cereal cropping of southern Queensland soils previously supporting native vegetation have resulted in reduced soil nitrogen supply, and consequently decreased cereal grain yields and low grain protein. To enhance yields and protein concentrations of wheat, management practices involving N fertiliser application, with no-tillage and stubble retention, grain legumes, and legume leys were evaluated from 1987 to 1998 on a fertility-depleted Vertosol at Warra, southern Queensland. The objective of this study was to examine the effect of lucerne in a 2-year lucerne–wheat rotation for its nitrogen and disease-break benefits to subsequent grain yield and protein content of wheat as compared with continuous wheat cropping.Dry matter production and nitrogen yields of lucerne were closely correlated with the total rainfall for October–September as well as March–September rainfall. Each 100 mm of total rainfall resulted in 0.97 t/ha of dry matter and 26 kg/ha of nitrogen yield. For the March–September rainfall, the corresponding values were 1.26 t/ha of dry matter and 36 kg/ha of nitrogen yield. The latter values were 10% lower than those produced by annual medics during a similar period. Compared with wheat–wheat cropping, significant increases in total soil nitrogen were observed only in 1990, 1992 and 1994 but increases in soil mineralisable nitrogen were observed in most years following lucerne. Similarly, pre-plant nitrate nitrogen in the soil profile following lucerne was higher by 74 kg/ha (9–167 kg N/ha) than that of wheat–wheat without N fertiliser in all years except 1996. Consequently, higher wheat grain protein (7 out of 9 seasons) and grain yield (4 out of 9 seasons) were produced compared with continuous wheat. There was significant depression in grain yield in 2 (1993 and 1995) out of 9 seasons attributed to soil moisture depletion and/or low growing season rainfall. Consequently, the overall responses in yield were lower than those of 50 kg/ha of fertiliser nitrogen applied to wheat–wheat crops, 2-year medic–wheat or chickpea–wheat rotation, although grain protein concentrations were higher following lucerne.The incidence and severity of the soilborne disease, common root rot of wheat caused by Bipolaris sorokiniana, was generally higher in lucerne–wheat than in continuous wheat with no nitrogen fertiliser applications, since its severity was significantly correlated with plant available water at sowing. No significant incidence of crown rot or root lesion nematode was observed. Thus, productivity, which was mainly due to nitrogen accretion in this experiment, can be maintained where short duration lucerne leys are grown in rotations with wheat.

Effects of repeated annual application and residual effects of past phosphorus (P) applications were studied at Billa Billa and The Gums, Queensland, on 2 Vertisols representative of a large cropping area in this region. Phosphorus was applied annually at 0, 4, 8, 12, and 25 kg/ha at sowing to each wheat crop between 1978 and 1988. Phosphorus was also applied at 25, 50, 100, 200, or 400 kg/ha as a once-only application, before wheat was sown in 1978, and was incorporated by tillage. Pot experiments were conducted each year with soil (6 kg/pot) gathered from field plots in May before wheat sowing to determine the residual value (RV) of previously applied P fertiliser under standard conditions of frequent watering. In 1979 the RV was determined in a second series of pots with a water deficit to simulate conditions of plant moisture stress that were to dominate the field experiments. The RV of P fertiliser was reduced to one-third that determined under well-watered conditions. Low residual values (8–47%) determined in the field in 1979 for P rates 25 and 50 kg/ha applied in 1978 were probably due to reduced P uptake from dry topsoil throughout which P residues were incorporated by tillage. By contrast, P applied annually at a low rate (4 or 8 kg/ha) in a band close to seeds created profitable responses when evaluated over the sequence of successive wheat crops. The bicarbonate-extractable soil test value (Pbf) on either soil fertilised annually for n years with P at a rate R (kg/ha· year) was described by the model where Pbu is the soil test value (mg/kg) of unfertilised soil.

Three field experiments were conducted on the Darling Downs (Queensland) to evaluate fertilizer management practices such as application depth and addition of nitrification inhibitor (N-serve), for nitrogen (N) applied in the February-May fallow period for winter cereals. Anhydrous ammonia or urea was applied in February, March or May at two depths (7 or 17 cm), with or without N-serve. Soil fertilized in February generally had a lower mineral-N content at sowing than soil fertilized in May. Deeper application (17 cm) in February did not increase soil mineral-N content to 0.2 m depth in May but addition of N-serve did at one site where it appeared to slow the movement of mineral N into the subsoil (0.2-0.4 m). A companion experiment was conducted at each site in which 15N-enriched urea was applied to a small (1 m2) area at the centre of a 4 m2 fertilized plot. Effects of fertilizer placement and N-serve treatment, as were used in field experiments, were evaluated in terms of crop recovery of 15N and total 15N recovery in plant and soil at harvest. Recovery of 15N by wheat, sown at two sites in June, showed that neither fertilizer management practice, application depth nor N-serve affected 15N recovery. At only one site did wheat recover less February-applied N than May-applied N. N-serve had no effect on 15N recovery by sorghum sown in October, of N applied in February or May, but 15N recovery was increased by deeper fertilizer placement. Total recovery of 15N in soil and plant after wheat harvest was lower (-74%) for February-application than for May-application (>94%). Similarly, total 15N recovery after sorghum was lower the earlier the fertilizer was applied. Unrecovered 15N was presumed lost due to denitrification during periods of temporary waterlogging of surface soil. Use of N-serve with the fertilizer application had no effect in conserving 15N applied for wheat or sorghum. However, deeper (17 cm) placement of N than normal (7 cm) promoted higher total recoveries, and therefore reduced losses, of applied 15N at the three sites.

Measurements of multiplication in liquid culture indicated that fast-growing Lotus rhizobia (Rhizobium loti) were tolerant of acidity and aluminium (at least 50 μM A1 at pH 4.5). Slow-growing Lotus rhizobia (Bradyrhizobium sp. (Lotus)) were less tolerant of acidity but equally tolerant of A1. Both genera were able to nodulateLotus pedunculatus in an acid soil (pH 4.1 in 0.01M CaCl2) and the slow-growing strains were more effective than the fast-growing strains in this soil over 30 days.

Effects of factors associated with soil acidity (low pH, low calcium, high aluminium and high manganese) on theTrifolium repens-Rhizobium trifolii symbiosis were investigted under laboratory conditions using an axenic solution-culture technique. 200 μM manganese increased root elongation in the range pH 4.3–5.5, but had no effect on root hair formation, the number of Rhizobium in the rhizosphere, or nodule formation. Root elongation and root hair formation were unaffected at pH 4.3 when 500 or 1000μM calcium was supplied, whereas multiplication of Rhizobium in the rhizosphere and nodulation were inhibited at pH 4.3 and 4.7.50–1000μM calcium had no effect either on the multiplication of Rhizobium in the range pH 4.3–5.5, or on nodule formation in the absence of aluminium.

Mixed-phase (heterogeneous) and single-phase (homogeneous) DNA subtraction-hybridization methods were used to isolate specific DNA probes for closely related Rhizobium loti strains. In the heterogeneous method, DNA from the prospective probe strain was repeatedly hybridized to a mixture of DNA from cross-hybridizing strains (subtracter DNA) which was immobilized on an epoxy-activated cellulose matrix. Probe strain sequences which shared homology with the matrix-bound subtracter DNA hybridized to it, leaving unique probe strain sequences in the mobile phase. In the homogeneous method, probe strain sequences were hybridized in solution to biotinylated, mercurated subtracter DNA. Biotinylated, mercurated subtracer DNA and probe strain sequences hybridized to it were removed by two-step affinity chromatography on streptavidin-agarose and thiol-Sepharose. The specificity of the sequences remaining after subtraction hybridization by both methods was assessed and compared by colony hybridization with R. loti strains. Both methods allowed the rapid isolation of strain-specific DNA fragments which were suitable for use as probes.

Effects of aluminium on theTrifolium repens var Huia-Rhizobium trifolii strain HP3 symbiosis were studied using an axenic solution-culture system. With, 10 μM phosphate, 50 μM aluminium reduced or inhibited root elongation at pH

The role of animals in society is well recognised. The programme director of the Tavistock Institute of Human Relations has emphasised the key role of the pet and stated that ". . . within the family the animal provides opportunities for projection and displacement of feelings as well as for direct expression of con cern and care, of anxiety and fear; and for testing out capacities for power, authority and influence within the family context."' The medical contribution which may be made by pets has not, perhaps, been fully appreciated until recently. There is now, however, evidence that the pet animal may play a part in the treatment and care of some patients. Workers in the field of psychotherapy have particularly emphasised the value of pets and Corson et al2 reported encouraging results when psych iatric patients in hospital were brought into close contact with dogs. Investigations into the psychotherapeutic value of cage birds to old people' showed that the presence of budgerigars generally had a beneficial effect. The role of pets in child development was first emphasised over 70 years ago4 and has since been investigated by many workers, including Levinson,5 and this is now reflected in the widespread use of animals in schools.6 They have proved particularly valuable in teaching mentally handicapped children.8 Many social workers and occupational therapists testify to the practical benefits that may ensue from encouraging contact between children and pets, and it is no coincidence that children's wards now frequently house a pet hamster, cagebird, or goldfish. Against these points, however, are the various arguments of those who, for one reason or another, oppose close contact between man and animals. Considerable concern is justifiably expressed over zoonoses, many of which are transmissible from pets to man. In addition public criticism is often levelled against domestic animals because they smell, cause traffic accidents, foul pathways, or make too much noise. Such argu ments may influence the decisions of those who have to decide whether or not animals are kept in a hospital. Other justifiable criticisms of pets in the hospital may be levelled because of expense or because animals are both timeand space-consuming. These and other objections have to be remembered whenever the question of animals in hospitals is raised. Whether keeping such animals is desirable is debatable but I intend to draw attention to some of the problems and pitfalls of maintaining animals under such circumstances and to make basic recom mendations regarding their care. While primarily intended for guiding those working in hospitals, this paper may also prove a useful guide for those who maintain animals in penal institu tions and educational establishments. Choice of animal

Hybridization of crushed Lotus pedunculatus root nodules with 32 P-labeled total genomic DNA probes was used to identify Rhizobium loti and Bradyrhizobium sp. ( Lotus rhizobia). Probes always hybridized with homologous target DNA and frequently with DNAs of other strains from the same genus. Intergeneric hybridization did not occur. Results were comparable to those from colony hybridization.

A novel subtraction hybridization procedure, incorporating a combination of four separation strategies, was developed to isolate unique DNA sequences from a strain of Rhizobium leguminosarum bv. trifolii. Sau3A-digested DNA from this strain, i.e., the probe strain, was ligated to a linker and hybridized in solution with an excess of pooled subtracter DNA from seven other strains of the same biovar which had been restricted, ligated to a different, biotinylated, subtracter-specific linker, and amplified by polymerase chain reaction to incorporate dUTP. Subtracter DNA and subtracter-probe hybrids were removed by phenol-chloroform extraction of a streptavidin-biotin-DNA complex. NENSORB chromatography of the sequences remaining in the aqueous layer captured biotinylated subtracter DNA which may have escaped removal by phenol-chloroform treatment. Any traces of contaminating subtracter DNA were removed by digestion with uracil DNA glycosylase. Finally, remaining sequences were amplified by polymerase chain reaction with a probe strain-specific primer, labelled with 32P, and tested for specificity in dot blot hybridizations against total genomic target DNA from each strain in the subtracter pool. Two rounds of subtraction-amplification were sufficient to remove cross-hybridizing sequences and to give a probe which hybridized only with homologous target DNA. The method is applicable to the isolation of DNA and RNA sequences from both procaryotic and eucaryotic cells.