Upper urinary tract stone disease is widespread in the developed world. On both clinical and economic grounds it is now accepted that evidence-based medical intervention is the only approach likely to make a significant impact on the incidence, and more importantly, the recurrence rates of this disease. Targeted medical prophylaxis requires reliable information on stone type which, when combined with relevant blood and urine analyses, allows identification of treatable risk factors. Data from an external quality assurance scheme indicate that stone analysis is poorly performed in many laboratories, and it is probable that this results in ill-informed patterns of investigation, inappropriate therapy, missed diagnoses of rarer causative disorders and wasteful further investigation of 'non-renal' stone artefacts. Renal stone analysis is a specialist investigation requiring appropriate analytical and interpretative expertise if the information is to be used to enhance patient care. For those laboratories not able to offer this, for whatever reason, referral is the only defensible approach to service provision. The methods currently employed in many departments have no place in modern clinical biochemistry practice.

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These results suggest a multifactorial aetiology for stone formation in renal transplant recipients. Approaches to prevention and management are discussed.

SUMMARY. We have developed a sensitive assay for the measurement of alanine:glyoxylate aminotransferase (EC 2.6.1.44) activity in human liver. The assay is partly automated, and takes into consideration the sensitivity of the reaction to pH and to glyoxylate concentration. It is less subject to interference from other enzymes utilizing glyoxylate and to chemical interference from glyoxylate itself and can therefore be used without correction for cross-over by glutamate:glyoxylate aminotransferase (EC 2.6.1.4). The assay allows clear discrimination between normal and affected livers and is sufficiently sensitive to measure enzyme activity in fetal liver samples. Enzyme activity ranged from 17·9 to 38'5/lmol/h/mg protein in control livers (n = 9) and 0·8 to 9·5 /lmol/h/mg protein in 30 of 39 hyperoxaluric patients studied. Normal alanine: glyoxylate aminotransferase activity (from 22·8 to 45·5/lmol/h/mg protein) allowed exclusion of primary hyperoxaluria type I in the other nine hyperoxaluric patients.