Amlodipine, a new long-acting dihydropyridine calcium antagonist, was compared with placebo and atenolol in 125 patients with mild to moderate systemic hypertension [supine diastolic blood pressure (DBP) 90-114 mm Hg]. Patients received placebo for 4 weeks, followed by a random allocation to an 8-week double-blind, once-daily treatment with amlodipine (n = 41), atenolol (n = 43), or placebo (n = 41). The changes in 24-h post-dose blood pressure (BP) from baseline to final visit for amlodipine (mean daily dose 8.8 mg, range 5-10 mg) were -12.8 +/- 2.0/ -10.1 +/- 1.2 mm Hg in supine BP and -11.5 +/- 2.3/-9.8 +/- 1.1 mm Hg in standing BP (p less than 0.001); for atenolol (mean daily dose 83.7 mg, range 50-100 mg), the changes from baseline were -11.3 +/- 2.3/-11.7 +/- 1.3 mm Hg in supine BP and -13.3 +/- 3.1/-12.3 +/- 1.5 mm Hg in standing BP (p less than 0.001); for placebo, the changes from baseline were -0.9 +/- 2.8/-3.5 +/- 0.9 mm Hg in supine BP and -1.6 +/- -2.6/-4.0 +/- 1.0 mm Hg in standing BP. In the study, goal response was defined as a supine DBP of less than 90 mm Hg or its decrease by greater than or equal to 10 mm Hg. The response rates were similar for atenolol (65%) and amlodipine (61%). Both active therapies were significantly more effective than placebo. Heart rate was significantly lowered by atenolol only.(ABSTRACT TRUNCATED AT 250 WORDS)