Felodipine is a new dihydropyridine calcium antagonist which selectively relaxes vascular smooth muscle. It lovers dose-dependently blood pressure in hypertensives patients. In this multicentre double-blind study, 113 patients (mean age 50 +/- 14 years) whose diastolic blood pressure was higher than 95 mmHg after withdrawal of an eventual antihypertensive therapy and a week of placebo administration. The patients received randomly either felodipine (5 mg x 2/j during two weeks and then 10 mg x 2/day) either atenolol (100 mg/day) during two months. Antihypertensive effects of these two drug regimens were not significantly different. Supine blood pressure decreased from 177 +/- 22/107 +/- 8 mmHg to 152 +/- 27/91 +/- 13 mmHg with felodipine and from 176 +/- 19/107 +/- 8 to 152 +/- 24/91 +/- 12 with atenolol. Side effects recorded by means of active questioning were ankle oedemas and headache with felodipine and fatigue and headache with atenolol.