Effect of an angiotensin inhibitor (AAS; loading dose of 25, 50, $100{mu}g/kg$ and maintenance dose of 12.5, 25,$50{mu}g/ka/hr$) on the pharmacokinetics of propranolol (4 mg/kg i.v.) was studied in rabbits. Plasma concentrations and relative bioavailability of propranolal increased upto 127-175% by AAS coinjection. The urinary excretion of propranolol decreased by AAS. Dosage regimen of propranolol should be adjusted when it is administered with AAS.