Amlodipine and nitrendipine are calcium antagonists of the 1,4-dihydropyridine group which differ in their pharmacokinetic and pharmacodynamic properties. The clinical relevance of these differences was investigated in a study designed to compare the efficacy and safety of once-daily amlodipine (5 mg) and nitrendipine (20 mg) in patients with mild-to-moderate essential hypertension. Ambulatory blood pressure monitoring and conventional measurements showed that amlodipine and nitrendipine produced comparable reductions in blood pressure after 4 weeks of treatment. However, the onset of the antihypertensive effect was gradual for amlodipine, while most of the reduction achieved at the end of treatment with nitrendipine was seen after the first dose. There were no significant changes in heart rate with amlodipine, but significant increases occurred during the first 6 h of nitrendipine treatment. Amlodipine was associated with a significantly lower incidence of vasodilator-related adverse effects at initiation of therapy (headache, flushing, tachycardia) compared with nitrendipine, which may reflect its slower onset of action. The different pharmacodynamic and toleration profiles of amlodipine and nitrendipine at therapeutically equivalent doses suggest that amlodipine may have advantages in the treatment of hypertension, especially in terms of the low incidence of acute side effects, which may ultimately translate into improved patient compliance.