This is the first reported large clinical trial of the antianginal and acute ischemic effectiveness and safety of dilevalol (the R, R-isomer of labetalol) in patients with chronic stable angina pectoris. This was a multicenter double blind fixed-dose parallel group placebo controlled trial. Patients with chronic stable angina and positive and reproducible exercise tests (+/- 20%) were included. If randomized, patients entered one of four fixed dose groups (twice a day placebo, 100 mgm, 200 mgm and 400 mgm bid for 2 weeks). Exercise testing was performed at 2 hours (peak) and 12 hours (trough) postdosing. This was followed by a 2-week once-a-day dosing regimen in which patients received the same total daily dose as the prior 2 weeks, with the full dose in the morning and a matched placebo in the evening. Exercise testing was performed at 2 hours (peak) and 24 hours (trough) postdosing. Anginal frequency and NTG consumption were significantly reduced, and equally so, by qd and bid regimens. The time of exercise to the onset of angina increased and the proportion of patients terminating exercise because of moderate angina decreased in a dose response fashion for both peak and trough tests and for both qd and bid regimens. There was also a dose related decrease in exercise induced ST segment depression and an increase in time to 1 mm ST depression. In 15 patients, 24-hour ambulatory monitoring also revealed a decrease in episodes of silent ischemia. No significant side effects related to the study drug occurred.(ABSTRACT TRUNCATED AT 250 WORDS)