The antihypertensive efficacy of the calcium entry blocker nitrendipine administered as monotherapy (20-80 mg; mean, 36/day) on the average for 144 days to 46 patients with essential hypertension (WHO I and II) was investigated in relation to age, pretreatment blood pressure, and plasma renin activity. In addition, we compared the blood pressure responses to verapamil (n = 11) and nifedipine (n = 15) with those to nitrendipine. Nitrendipine monotherapy reduced blood pressure from 168 +/- 16/107 +/- 7 mm Hg to 145 +/- 13/91 +/- 6 (both p less than 0.001); in 33 of 46 patients a diastolic pressure less than or equal to 95 mm Hg was achieved. During long-term treatment, heart rate and body weight remained unchanged. Thirteen of 16 patients in whom blood pressure was measured 24 h after a single oral dose (20 to 40 mg) reached a diastolic pressure less than or equal to 95 mm Hg. Treatment with nitrendipine had to be discontinued because of severe headache in two and ankle oedema in one patient. The fall in mean blood pressure after nitrendipine was directly related to age (r = 0.553; p less than 0.001) and pretreatment mean blood pressure (r = 0.470; p less than 0.01) and inversely related to plasma renin activity (r = 0.558; p less than 0.001). These correlations were also significant for systolic and diastolic blood pressure. There was comparable antihypertensive efficacy, as expressed by changes in mean blood pressure, between nitrendipine and verapamil (r = 0.869; p less than 0.01), and nitrendipine and nifedipine (r = 0.953; p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)