Renal insufficiency is common in adults with homozygous sickle cell disease, and the contribution of glomerular failure to the hyperuricaemia which is often a feature of the disease has therefore been investigated. In a study of 64 patients between the ages of 15 and 66, serum urate concentration was dependent on renal urate clearance and also on creatinine clearance. The relation between serum urate and creatinine clearance was abnormal in patients with sickle cell disease and it is suggested that this might be caused by high single nephron glomerular filtration rates. Both the amount of urate excreted per millilitre of glomerular filtrate and the fractional excretion of urate increased with falling creatinine clearance, suggesting that the ability to increase tubular urate secretion was preserved. Patients with extensive tubular disease as shown by tubular proteinuria had serum urate concentrations which were not significantly different from those of age and sex matched non-proteinuric patients. Evidence that renal tubular disease interferes with urate secretion and causes hyperuricaemia in patients with sickle cell disease needs to be reinterpreted in the light of these findings.