1 Some cardiovascular pharmacology of prizidilol hydrochloride, a new antihypertensive compound with precapillary vasodilator and beta-adrenoceptor antagonist activity, in man is described. 2 To investigate further the pharmacological profile of this drug the effects of a single oral dose of 400 mg prizidilol hydrochloride were compared with propranolol 40 mg in combination with either 25 mg or 50 mg of hydralazine for up to 6 h after dosing, in a placebo controlled in eight healthy subjects. 3 Prizidolol hydrochloride significantly reduced supine and standing diastolic blood pressure and was more effective than propranolol combined with either dose of hydralazine in this respect. 4 Supine heart rate was significantly increased after prizidilol hydrochloride, but was not significantly changed after propranolol combined with either dose of hydralazine. The reasons for the increase in supine heart rate after prizidolol are discussed. 5 beta-adrenoceptor antagonism was assessed in terms of inhibition of exercise induced increases in heart rate and systolic blood pressure. At the doses used, prizidolol hydrochloride was less effective than propranolol and hydralazine combined, particularly during the first 3 h after dosing.