Recently, bisoprolol has been investigated regarding its effects on exercise tolerance and the duration of action in patients with coronary heart disease (CHD) following single oral administration. It appears, however, that the extent of effects of 5 mg bisoprolol is not fully established yet. Therefore, the effects of 5 and 10 mg bisoprolol and the duration of action were assessed in 12 patients (10 male, 2 female; mean age 60.2 years) with stable angina pectoris due to CHD after repeated administration. Patients were given 5 or 10 mg bisoprolol once daily for 2 weeks according to a double-blind, randomized cross-over design. At entry one exercise tolerance test (ETT) served as baseline measurement and following each treatment period ETTs were performed before (24-hour value) and 3 hours after tablet intake. Exercise capacity (in W X min) was calculated until the onset of angina, 0.1 mV ST-segment depression and at peak exercise. Compared to baseline all workload values during active therapy were significantly improved (P less than or equal to 0.05) except for the workload till onset of angina with bisoprolol 5 mg at 24 hours. The effects at 3 hours were significantly stronger than those after 24 hours for both dosages. Significantly stronger effects were observed 3 hours as well as 24 hours after intake during treatment with 10 mg compared to 5 mg: at peak exercise on heart rate (P less than or equal to 0.05) and exercise capacity (P less than or equal to 0.01), at identical workload on heart rate (P less than or equal to 0.01) and rate-pressure product (P less than or equal to 0.01). It was found that bisoprolol 5 mg once daily leads to therapeutic effects with a clearly maintained duration of action over 24 hours, but further increase of peak exercise capacity may be achieved with 10 mg.