Twenty-seven hypertensive outpatients were studied to evaluate the efficacy of verapamil after a single oral dose as well as following a short-term treatment and also in combination with oxprenolol. Blood pressure was significantly reduced (p 0.01) after verapamil monotherapy and the combined treatment. PR interval was lengthened from 30 min to 4 h during acute testing, and also after short-term treatment. QT was only prolonged after the verapamil monotherapy. Systolic time intervals (STIs) were not modified, except left ventricular ejection time (LVETc). Direct correlations were found among verapamil plasma concentrations and changes provoked on blood pressure and PR interval. The mean side effects found were disturbance of atrioventricular conduction in two patients without ulterior complications. The results suggest that verapamil monotherapy or in combination with oxprenolol could be useful in the treatment of essential hypertension.