The antihypertensive efficacy and safety of amlodipine (5-10 mg once daily for 10 weeks) was assessed in elderly patients with primary systolic hypertension (average sitting and standing systolic blood pressure > or = 160 mm Hg and diastolic blood pressure < or = 95 mm Hg). Interim analysis of data from 25 patients shows that amlodipine treatment produced significant decreases in sitting blood pressure (-26.8/-11.4 mm Hg; p < 0.05). Efficacy assessments after 8 weeks of therapy showed 15 of 21 (71.4%) evaluable patients were considered therapeutic successes with amlodipine (defined as a fall from baseline in sitting systolic blood pressure of > or = 20 mm Hg or to < or = 150 mm Hg with a fall of > or = 10 mm Hg). Of the six evaluable patients who were not considered therapeutic successes using this definition, three had clinically beneficial falls in systolic blood pressure of 16-18 mm Hg. Fourteen patients were considered therapy successes on the basis of assessments taken 48 h postdose at the end of the study. Investigators' overall impression of efficacy was excellent or good in 21 patients (84%). Amlodipine treatment had no significant effect on heart rate. Amlodipine was generally well tolerated, with no patients being withdrawn due to side effects. Investigators' evaluation of toleration was excellent or good in 22 patients (88%).