Calcium channel blocking agents are considered to be particularly effective in reducing blood pressure (BP) in low renin essential hypertension and in primary aldosteronism. The aim of this study was to compare the acute BP response to nicardipine in 2 opposite situations of stimulation of the renin angiotensin system: eight patients (49 +/- 13 years, mean arterial BP (MAP) 123 +/- 8 mmHg) with primary aldosteronism (active renin less than 5 pg/ml, group 1) and nine patients (38 +/- 17 years, MAP: 107 +/- 13 mmHg) with renovascular hypertension and high level of active renin (greater than 25 pg/ml, group 2). They had not taken any antihypertensive treatment since at least one week. After 60 minutes in the supine position (T0) nicardipine was infused at a rate of 7.5 mg/h during 10 minutes (T10), 15 mg/h from the 10th to 20th minute (T20) and 30 mg/h during the last ten minutes (T30). Thus, a total cumulative dose of 8.75 mg was administrated in 30 minutes. BP was recorded by an indirect oscillometric method (Sentrom) every 2 minutes and renin was assayed through an immuno-radiometric procedure (IRMA). There was an important and similar BP fall in the 2 groups (Gr 1: T10-6 p. 100, T20-17 p. 100, T30-25 p. 100; Gr 2: T10-7 p. 100, T20-13 p. 100, T30-18 p. 100) with a very significant dose-effect relation (r = 0.67, p less than 0.001). There was also an important increase in heart rate similar in the 2 groups (+35 p. 100, +25 p. 100, ns).(ABSTRACT TRUNCATED AT 250 WORDS)