One hundred and one hypertensive patients [diastolic pressure (dBP) 95-110 mm Hg after greater than or equal to 6 weeks with no antihypertensive therapy] were randomized to receive, double-blind, felodipine-ER 5 mg once daily (n = 49) or placebo (n = 52) for 2 weeks. Twenty-four hours post-dose, felodipine-ER 5 mg o.m. reduced dBP by a mean of 11 mm Hg; in contrast, dBP fell in the placebo group by 3 mm Hg (p less than 0.001). If the target dBP of less than or equal to 90 mm Hg was not attained at 2 weeks, the dose of felodipine-ER (or placebo) was doubled; if the target was not attained after a further 2 weeks, the doses were doubled again, to 20 mg felodipine-ER or placebo. If the target was achieved after 2 or 4 weeks, patients remained on that dose; the double-blind period for all patients was 6 weeks. After 6 weeks, the mean reduction in dBP in the felodipine-ER group was 14 mm Hg, significantly (p less than 0.001) greater than in the placebo group (8 mm Hg). Blood pressure "control" was defined prospectively as a seated dBP less than or equal to 90 mm Hg: after 6 weeks, 67% of patients receiving felodipine-ER compared with 27% on placebo had a controlled blood pressure (p less than 0.001). The figures after 2 weeks were 45% on 5 mg felodipine-ER and 21% on placebo (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)