1. The renal clearance of [ 14 C]oxalate was assessed by the constant-infusion technique and single-injection technique (plasma sampling only: one-compartment and two-compartment model; plasma and urine sampling). Healthy volunteers and patients with renal stones were studied. 2. Results with the constant-infusion techniques (with and without urine sampling) were not significantly different from each other. 3. The renal clearance of [ 14 C]oxalate measured with the single-injection technique as compared with the constant-infusion technique was overestimated in the single-injection one-compartment model (52%) as well as in the two-compartment model (30%). 4. The calculated level of plasma oxalate in the healthy volunteers ranged from 1·04 to 1·78 μmol/l (mean 1·39). 5. The biological half-life of [ 14 C]oxalate, estimated by the cumulative excretion of 14 C in urine after equilibrium had been established, was 128 min (range: 113–142). 6. The oxalate/creatinine clearance ratio in the healthy volunteers ranged from 1·73 to 2·22 (mean 2·01).