In a multicenter, dose-ranging, double-blind study, 63 patients diagnosed as having stable angina pectoris were randomly assigned to treatment with carteolol (33 patients) or nadolol (30 patients). Following a 2 to 4-week dose-ranging period, an optimal dose was determined for each patient and treatment with that dose continued for 6 weeks. Data from all 63 patients were analyzed for drug safety; data for 52 patients (27 carteolol and 25 nadolol) were analyzed for drug efficacy. The most commonly chosen dosage levels were 20 mg of carteolol and 80 mg of nadolol. There were no statistically significant differences between the carteolol and nadolol groups in changes in exercise tolerance as reflected by time to onset of angina, end-point of exercise, and onset of 1 mm ST segment change on ECG. Both drugs significantly suppressed tachycardia and double product during treadmill exercise. The nadolol-treated group demonstrated a significantly greater reduction in resting heart rate (18.7 bpm) as compared with the carteolol-treated group (3.1 bpm). Carteolol possesses intrinsic sympathomimetic activity (ISA), which may account for the fact that carteolol effectively reduces exercise-induced tachycardia while producing relatively little effect on resting heart rate. The frequency of anginal attacks and the use of sublingual nitroglycerin were reduced to a similar extent in both treatment groups. The most commonly reported side effect in both treatment groups was asthenia.(ABSTRACT TRUNCATED AT 250 WORDS)