Effects of propranolol on the pharmacokinetics of cyclosporine were investigated after intravenous and oral administration of the drugs to control rats and rats with uranyl nitrate-induced acute renal failure (U-ARF). Effects of intravenous propranolol, 3 mg/kg, on the pharmacokinetics of intravenous cyclosporine, 3 and 30 mg/kg, to control rats, and 30 mg/kg, to rats with U-ARF seemed to be negligible. However, the effects of orally administered propranolol, 10 mg/kg, on the area under the blood concentration-time curve (AUC) of oral cyclosporine were significant after oral administration of cyclosporine, 10 and 100 mg/kg, to control rats. For example, the AUC of cyclosporine increased significantly (33.1 versus 24.7 microg h/ml) at cyclosporine oral dose of 10 mg/kg, however, the value decreased significantly (167 versus 235 microg h/ml) at cyclosporine oral dose of 100 mg/kg. Effects of orally administered propranolol, 10 mg/kg, on the pharmacokinetics of orally administered cyclosporine, 100 mg/kg, seemed to be negligible in rats with U-ARF.