A double-blind, stratified and randomized multicentre trial was carried out to compare the antihypertensive efficacy of nitrendipine with that of propranolol. The dose of nitrendipine was 5-20 mg b.d., and of propranolol, 40-120 mg b.d. With nitrendipine (N = 137), systolic blood pressure (SBP) and diastolic blood pressure (DBP) fell from 156 +/- 1 to 140 +/- 1 mmHg and from 101 +/- 0 to 89 +/- 1 mmHg respectively (mean +/- SEM) (P less than 0.0001). On propranolol (N = 138), SBP fell from 156 +/- 1 to 144 +/- 2 mmHg and DBP decreased from 101 +/- 0 to 91 +/- 1 mmHg (P less than 0.0001). In a subgroup of 11 patients on nitrendipine, mean 24-hour SBP dropped from 137 +/- 4 to 128 +/- 4 mmHg and DBP fell from 92 +/- 2 to 87 +/- 2 mmHg (P less than 0.01). On propranolol, mean 24-hour SBP and DBP were decreased from 142 +/- 4 to 128 = 4 mmHG (P less than 0.05) and from 89 +/- 2 to 84 +/- 2 mmHg (P less than 0.09), respectively. Plasma renin activity was not altered significantly by nitrendipine (N = 89), but was significantly reduced from 1.86 +/- 0.24 to 1.37 +/- 0.75 ng ml-1 h-1 by propranolol (N = 88, P less than 0.002). Plasma renin activity was inversely correlated with age, but was not related to the reduction of SBP or DBP.(ABSTRACT TRUNCATED AT 250 WORDS)