The antihypertensive efficacy of once-daily amlodipine was studied in a group of 30 patients with mild to moderate hypertension in a double-blind, placebo-controlled, parallel-group study. The dose range of amlodipine was 2.5-10.0 mg daily adjusted every 2 weeks for a total treatment period of 8 weeks. Amlodipine produced a significant reduction in blood pressure compared with placebo, the mean difference between baseline and 8 weeks (corrected for placebo effect) being 16/12 mm Hg supine, 14/4 mm Hg standing. Blood pressure returned to baseline values during a terminal 4-week washout period with placebo. There were no significant effects on heart rate. Two patients experienced slight ankle edema while receiving amlodipine 10.0 mg daily but the active drug was otherwise well tolerated.