The antihypertensive efficacy of calcium antagonists could depend on the concentration of circulating renin. To investigate this hypothesis, 102 hypertensive men or women were included in this study. After an initial 2 week placebo period, the patients were administered slow-release nicardipine, 50 mg twice a day for twelve weeks. The blood pressures were measured with a mercury sphygmomanometer at inclusion (S2) and after 12 weeks of treatment (S14), in addition to home automeasure during the week before inclusion and the two weeks preceding the final visit. The plasma renin activity (RA) was measured at S2 and S14. Its value at inclusion was used to differentiate patients with low renin (< or = 11 ng/l) from those with normal (> 11 < or = 17 ng/l) or high renin activity (> 17 ng/l). The blood pressure measured by sphygmomanometer or automeasure was significantly lower at the end of the active treatment period (SBP: -8 mmHg; DBP: -9.5 mmHg; and SBP: -5.8 mmHg; DBP: -5.7 mmHg respectively); the reduction in blood pressure was significantly higher in the group with low RA than in the group with high RA. The reductions in SBP measured in the morning and evening and in DBP measured in the morning were significantly greater in the group with low RA than in the group with high RA. The reduction of SBP measured in the morning at midday, and in the evening was correlated to the basal value of RA. Mild side effects were observed in 20 patients leading to the interruption of treatment in 11 cases because of headache. The best antihypertensive response is observed in patients with low plasma RA. This could explain the good response to calcium antagonists usually observed in elderly hypertensives.