The effects on heart rate, blood pressure and pulmonary function of single oral doses of prizidilol hydrochloride (400 mg SK&F 92657) and propranolol (40 mg) were compared with placebo in nine healthy volunteers, in a double blind crossover study. Prizidilol had no effect on heart rate while propranolol caused a significant reduction compared with placebo. Diastolic blood pressure was lowered to the same extent by both prizidilol and propranolol. Propranolol significantly reduced the forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC) and the maximal expiratory flow at 50% vital capacity (MEF 50). Prizidilol had no effect on flow-volume loop parameters. Effective pulmonary blood flow was not altered by propranolol, but it was significantly increased by prizidilol. Oral prizidilol exerts its hypotensive effect by vasodilatation without reflex tachycardia. It does not cause airways obstruction in healthy subjects.