A total of 178 patients participated in a 14-week, multicenter, double-blind, parallel study to evaluate the comparative efficacy and safety of single daily doses of 200, 300 and 400 mg of bepridil hydrochloride and placebo in the treatment of patients with chronic stable angina pectoris. The results showed that weekly angina attacks and nitroglycerin consumption were significantly reduced from baseline levels with all doses of bepridil (p less than 0.01), and the reductions were consistently greater than those in the placebo group. For the 400-mg dose the reductions in angina attacks and nitroglycerin consumption were significantly greater (p less than or equal to 0.05) than those in the placebo group at all but 1 evaluation point. Exercise tolerance improved significantly during bepridil administration (p less than or equal to 0.05), and a significant linear dose response was noted for total exercise time, total work and time to onset of angina. In addition, bepridil was significantly superior to placebo for these parameters at doses of 300 (p less than or equal to 0.05) and 400 mg (p less than or equal to 0.01). There were small reductions in heart rate (mean 3.7 beats/min) and prolongation of QT and QTc intervals (approximately 30 to 40 milliseconds) associated with bepridil treatment. Bepridil was well tolerated by patients in this study. When adverse effects occurred, they most frequently involved the gastrointestinal and central nervous systems. Of the patients receiving bepridil, 6% discontinued therapy because of adverse effects.(ABSTRACT TRUNCATED AT 250 WORDS)