Sixteen hydralazine-dependent hypertensive patients (7 females) were included in this clinical study. All patients were being treated with hydralazine, cyclopenthiazide and propranolol in the first visit to the laboratory. Two drugs were maintained during the study: the beta blocker and the diuretic. Hydralazine was discontinued and replaced by placebo during 3 weeks and after this period, verapamil was instituted at increasing doses. Replacing hydralazine by verapamil a better control of hypertension was obtained with a daily dose of 400 mg. The calcium entry blocker causes shortening of PEPc interval probably by reducing afterload which was only observed with the highest dose of verapamil (400 mg). ECG intervals were not modified by the different treatments with the exception of PR which was significantly increased by the major dose of verapamil. The calcium antagonist produced a stable reduction of blood pressure without affecting left ventricular function.