Amlodipine, a novel dihydropyridine calcium-antagonist, was compared to slow-release nifedipine in a short-term study on 40 patients with mild to moderate essential hypertension, in order to assess the efficacy and tolerability of two different dihydropyridine calcium-antagonists with short and long half-life. After a two-week single-blind placebo period, patients were given, in a randomized sequence, amlodipine (5 or 10 mg/day od, 20 patients) or nifedipine s.r. (20 or 40 mg BID, 20 patients). At the end of treatment (12 weeks) a significant lowering of arterial pressure was obtained after 24h from the administration of amlodipin (-34/-17 mmHg) and after 12h from the administration of nifedipine s.r. (-33/-16 mmHg). Furthermore, with both drugs, no significant changes in heart rate and ECG have been reported. Amlodipine was better tolerated than nifedipine, as shown by the lower incidence of side effects. Therefore amlodipine proved to be an effective and well tolerated drug in the therapy of mild to moderate hypertension.