The ability of nitrendipine to control blood pressure (BP) over a 12- or 24-h period was assessed in patients greater than 65 years of age who had a systolic BP (SBP) greater than 170 mm Hg and a diastolic BP (DBP) greater than 100-130 mm Hg. Thirty patients were randomized equally into two groups: Group 1 received the drug once daily and Group 2 received it twice daily after a 2-week run-in on placebo. The study was double blind. BP was recorded 24 h (Group 1) or 12 h (Group 2) postnitrendipine. The study design permitted one dose titration if BP exceeded 170/100 mm Hg after 3 weeks of active therapy when the dose was doubled. Patients received 6 weeks of therapy at the preferred dosage. Patients underwent measurements of cerebral blood flow (CBF) initially and on three further occasions: after the final dose of placebo, and after the first and last doses of nitrendipine. With active therapy, mean SBP and DBP fell in both groups when subjects were in the sitting and standing postures, except that in Group 1 at Week 5 only, standing SBP and DBP were not significantly reduced on the 10 mg once daily regimen. At the preferred dose, eight of the 15 patients in Group 1 and 13 of the 15 patients in Group 2 responded with a reduction of standing DBP of 10 mm Hg or greater, 24 and 12 h, respectively, after the last dose.(ABSTRACT TRUNCATED AT 250 WORDS)