A double-blind, randomized study comparing the efficacy of intravenous acebutolol with propranolol on frequent premature ventricular complexes (PVCs) in 24 patients is reported. Frequent PVCs were abolished or reduced by 75% or more in 10 of 12 patients (83%) given acebutolol and in 10 of 12 patients (83%) given propranolol. The therapeutic effect of acebutolol lasted for at least 1 hr in 4 of 12 patients (33%), for at least 3.5 hr in 3 of 12 patients (25%), and for at least 4 hr in 2 of 12 patients (17%). The effect of propranolol lasted for at least 1 hr in 6 of 12 patients (50%), for at least 3.5 hr in 4 of 12 patients (33%), and for at least 4 hr in 4 of 12 patients (33%). Hence, intravenous acebutolol and propranolol were equally effective.