This randomized, double-blind, crossover study was aimed at detecting efficacy differences in blood pressure control and peripheral circulation in cerebral aortic and femoral districts of slow-release nicardipine, 40 mg, and captopril, 50 mg, given twice daily to 20 primary hypertensive patients (9 male, 11 female; age range 33-60 years) for a period of 4 weeks for each treatment. Blood flow velocities in the aorta, common carotid artery, internal carotid artery, middle cerebral artery, and common femoral artery were noninvasively measured using a 2.0- or 5-MHz Doppler probe. Systolic blood pressure fall was similar with nicardipine (from 156 +/- 12 to 139 +/- 8 mm Hg, p less than 0.001) and captopril (from 158 +/- 13 to 146 +/- 13 mm Hg, p less than 0.001) while significant efficacy difference (p less than 0.005) in diastolic pressure control was detected (from 104 +/- 6 to 91 +/- 8 mm Hg, p less than 0.001 with nicardipine and from 102 +/- 6 to 98 +/- 7 mm Hg with captopril). Regarding regional hemodynamics, nicardipine increased (from 119 +/- 24 to 133 +/- 27 cm/s), and captopril did not affect systolic velocity in the aorta (difference between final data, p less than 0.03). In the common carotid artery systolic velocity was increased solely by nicardipine. No significant changes were detected in the other vessels explored.(ABSTRACT TRUNCATED AT 250 WORDS)