Patients on cyclosporin A (CsA) often develop hyperuricaemia and gout. In transplant patients the use of uricosuric drugs for treating hyperuricaemia may be preferable to allopurinol because of the known interaction of the latter with azathioprine. We therefore prospectively studied the uricosuric efficacy of 100 mg benzbromarone (Bbr;Desuric) daily in 25 CsA-treated renal transplant patients with stable graft function and hyperuricaemia (> 359 mumol/l for females, > 491 mumol/l for males). Benzbromarone decreased plasma uric acid from 579 + 18 mumol/l to 313 +/- 24 mumol/l (mean +/- SEM; P < 0.0001) and thereby normalized plasma uric acid in 21 of 25 patients. The remaining four patients had creatinine clearances between 21 and 25 ml/min, the lowest of the entire study group. Mean fractional clearance of uric acid increased from 5.4 +/- 0.4% to 17.2 +/- 1.0% (P < 0.001). The relative decrease of plasma uric acid closely correlated with baseline creatinine clearance (r = 0.67; P < 0.001). CsA trough values were not influenced. None of the patients experienced any significant side-effects. As an unexpected find-ing, urinary uric acid excretion increased from 2082 +/- 175 mumol/24 h to 3233 +/- 232 mumol/24 h after 4 weeks' treatment with benzbromarone. In conclusion, benzbromarone normalized plasma uric acid in all CsA-treated renal transplant recipients with a creatinine clearance > 25 ml/min. Due to its excellent efficacy and lack of significant side-effects, benzbromarone appears to be preferable to allopurinol in CsA-treated renal transplant recipients with a creatinine clearance over 25 ml/min.