1. Plasma oxalate has been measured by a radioisotopic method applicable to all concentrations of plasma oxalate and renal function, and also by an enzymatic method which was only applicable to raised concentrations of plasma oxalate.
2. Where the two methods could be applied simultaneously, the agreement between them was good.
3. Plasma oxalate was 86% ultrafiltrable at concentrations of up to 44 μmol/l.
4. Oxalate clearance and the exchangeable oxalate pool were also measured. The ratio of oxalate clearance to creatinine clearance was greater than unity in most normal subjects and patients.
5. These methods were used in normal subjects and in patients with primary hyperoxaluria and/or chronic renal failure. A raised plasma oxalate concentration was found in both conditions. Chronic renal failure is probably the most common cause of a raised plasma oxalate.