The acute effects of the calcium entry blocker, nifedipine, on cerebral circulation were studied in 22 patients (56 +/- 5 years) with essential hypertension (EHT, WHO I-II) and 12 age-matched normal subjects. Cerebral effects were reevaluated in sixteen EHT patients after 8 weeks of treatment. The cerebrovascular resistance (Rp), cerebral capacitance (Cp), carotid velocity, and flow volume were measured by a newly developed ultrasonic volume flow meter coupled with a built-in computer which calculates Rp and Cp based on a simulated model. In EHT, acute administration of nifedipine (10 mg orally) decreased Rp from 13.5 +/- 1.8 to 8.0 +/- 0.3 (p less than 0.01) and increased Cp from 22.8 +/- 3.3 to 54.9 +/- 5.2 mFc (p less than 0.01). The carotid blood flow and velocity increased by 25.7% and 22.9%, respectively (p less than 0.05) in the face of lowered arterial pressure. In normal subjects, nifedipine also decreased Rp and increased Cp but to a lesser degree compared with EHT. The acute changes in cerebrovascular circulation in EHT were maintained at 8 weeks of treatment. These results suggest that nifedipine reduces Rp, possibly as the consequence of systemic hypotension and direct vasodilation of the cerebral arteries. This may be beneficial for hypertensive patients.