The beta-blocking and vasodilating agent carvedilol was compared with a combination of propranolol and isosorbide dinitrate (ISDN) in a double-blind, parallel-group study. After two baseline sitting bicycle exercise tests on placebo, 31 patients with chronic stable angina were asymmetrically randomized to treatment with carvedilol (25 mg b.i.d.) or propranolol-ISDN (80 mg/20 mg b.i.d.) for a period of 6 months. Further exercise tests were performed 2 h after the first dose as well as after 1, 3, and 6 months of treatment. Twenty-seven patients were considered evaluable for efficacy. Differences between the two groups were observed with emphasis on total exercise time and time to 1-mm ST-segment depression. In contrast to a greater peak effect of the first propranolol/ISDN dose, the chronic antianginal and anti-ischemic effects of carvedilol at trough were found to be more marked than those of the combination.