The effects of bopindolol, a new beta-adrenoceptor blocker, on the exercise tolerance of 12 in-patients, mean age 57 (5 years), with stable angina pectoris and documented coronary artery disease were evaluated. All patients received on 4 different days a single oral dose of bopindolol 0.5 mg, bopindolol 1.0 mg, bopindolol 2.0 mg and placebo according to a double-blind latin square design. Treadmill symptoms-limited exercise tests were performed using a Bruce protocol, 3, 12 and 24 h after dosing. Bipindolol improved (P less than 0.05) exercise tolerance in comparison with placebo (by a maximum of 33%, 52% and 26% after the 2.0 mg dose) with no adverse effect on ischaemia. The primary action of bopindolol appeared to be to reduce myocardial oxygen consumption (mainly by its negative chronotropic effect) for up to the 24th hour after oral administration. Eight (66%) patients were angina free at the 3rd, 12th and 24th h exercise test. The effects of bopindolol were not dose-related. A short period of inactivity due to hospitalization may have influenced the exercise performance and led us to underestimate the presence of a dose-response. The results of this report suggest that bopindolol has a long lasting effect in the treatment of patients with chronic stable angina pectoris.