In a randomized, double-blind, multicenter study, the efficacy of diltiazem controlled-release (CR) 120 mg b.i.d. was compared with metoprolol 100 mg b.i.d. in 56 patients with stable exertional angina pectoris. Fifty-one patients (28 receiving diltiazem CR, 23 receiving metoprolol), completed a follow-up period of 8 weeks. Thirty-nine patients (20 receiving diltiazem CR, 19 receiving metoprolol), completed a follow-up period of 32 weeks. Maximal exercise testing was performed at baseline and after 8, 20, and 32 weeks of treatment. Most exercise parameters were not significantly different between the patients on diltiazem CR and those on metoprolol. However, exercise duration was longer and maximal work load was higher in patients on diltiazem CR than in patients on metoprolol, and significant differences were observed at 20 weeks of treatment (p = 0.006 and p = 0.008, respectively). At all times during treatment, heart rate at maximal exercise and rate-pressure product at maximal exercise were significantly lower in the patients treated with metoprolol. In conclusion, monotherapy with diltiazem CR is at least as effective as monotherapy with metoprolol in patients with stable angina pectoris. As compared to metoprolol, diltiazem CR has a minor depressing effect on rate-pressure product, resulting in a favorable effect on exercise duration.