The pharmacokinetic parameters of cyclosporine (CsA) were determined in 23 kidney transplant recipients and 19 children with nephrotic syndrome, after intravenous and oral administration. The mean bioavailability was 39%, blood clearance was 0.55 l.h-1.kg-1 and volume of distribution at steady-state was 2.77 l.kg-1. The absorption profile was monophasic (67%), biphasic (29%) or poor (4%). The maximum blood concentration of CsA was significantly higher in children with a monophasic profile than in children with a biphasic profile (550 vs 380 ng.ml-1). Blood clearance was significantly higher in the transplant recipients than in the patients with nephrotic syndrome (0.65 vs 0.43 l.h-1.kg-1. Although age, haematocrit, creatinine clearance, serum albumin and cholesterol differed between the two groups, only haematocrit and creatinine clearance were significantly (negatively) correlated with CsA clearance.