Once-daily administration of amlodipine, a long-acting dihydropyridine calcium-channel blocker, and atenolol, a cardioselective beta-adrenoceptor blocking agent, were compared in patients with mild to moderate hypertension in a multicenter placebo-controlled trial. The starting dose of amlodipine was 2.5 mg, with upward adjustment to 5.0 mg and 10.0 mg at 2-weekly intervals; atenolol was started at 50 mg and titrated to 100 mg after 4 weeks. After 8 weeks of treatment, amlodipine and atenolol both reduced blood pressure to a statistically and clinically significant extent at 24 h postdose, and with a small trough-peak (i.e., 24 h to 8 h postdose) difference. Unlike atenolol, amlodipine had no effects on heart rate. The incidence of side effects was low. There were no clinically significant changes in serum lipids with either drug. It is concluded that once-daily dosing with either amlodipine or atenolol significantly reduces blood pressures. Both amlodipine and atenolol were well tolerated.