The antianginal efficacy of metoprolol OROS has been investigated in comparison with that of atenolol in a multicenter double-blind cross-over trial carried out in patients with stable effort angina. OROS (ORally OSmotic) is a new semi-permeable delivery system with very slow osmotic release of the active drug, which is maintained at virtually constant plasma levels throughout the 24 hours. At the end of a 2-week run-in period, 53 patients with chronic coronary artery disease and documented ischemia during bicycleergometric exercise test were given, on double-blind condition, metoprolol OROS 21/285 and atenolol 100 mg in random order for 4 weeks each. On the last day of each cross-over period, patients underwent a bicycleergometric exercise test 24 hours after the last drug intake. The mean number of anginal attacks (2.54 during the 2-week run-in period) decreased under both metoprolol OROS (1.29 and 1.13 after 2 and 4 weeks of treatment, respectively) and atenolol (1.29 and 0.73 after 2 and 4 weeks of treatment, respectively), with no difference between the two beta-blockers. The same behaviour was observed as regards the nitroglycerin tablets consumption. The exercise test variables (i.e. duration of exercise, maximum workload and peak exercise values of systolic and diastolic blood pressure, heart rate and ST-segment depression) did not differ between the two treatments and did not show a time-effect. The percentage of patients reporting adverse effects was low with both treatments. Two patients were withdrawn from the study during atenolol (gastralgia and heartburn, respectively), and one during metoprolol OROS (gastralgia).(ABSTRACT TRUNCATED AT 250 WORDS)