This open-label, multicenter study was designed to assess the efficacy and tolerability of once-daily amlodipine treatment and its effects on exercise test variables in patients with ss;able angina pectoris. A total of 233 patients with this condition (82 women, 151 men; mean age, 57 +/- 18 years) treated at 17 medical centers were enrolled in the study; 215 patients (92%) completed the study. A a-week baseline period in which the patients maintained their existing antianginal therapy was followed by a 10-week treatment period with 5 to 10 mg of amlodipine daily. Maximal treadmill exercise tests using the Bruce protocol were performed at the beginning and end of the amlodipine treatment period. After amlodipine therapy, both the median number and duration of anginal attacks per week and the median number of nitroglycerin tablets consumed per week were reduced significantly when compared with baseline values. During self-assessment, 81% of patients reported excellent or good anginal control, 14% reported moderate control, and 5% reported poor control with the drug. Systolic and diastolic blood pressures, heart rate, resting patterns on electrocardiography, and blood and urine analyses showed no statistically significant changes. Compared with baseline, amlodipine treatment significantly increased exercise duration and maximum workload attained, prolonged the time to onset of angina and ST-segment depression, and decreased the magnitude and duration of ST-segment depression. Maximum heart rate, systolic blood pressure detected during exercise testing, and calculated rate-pressure product did not change significantly with amlodipine treatment. Forty-four patients (19%) experienced adverse events considered to be drug related. The most commonly reported adverse events were headache and ankle edema. In three patients (1%) amlodipine treatment was discontinued due to the severity of the side effects. It is concluded that amlodipine, when added to existing antianginal drug therapy, is well tolerated, significantly reduces the incidence of anginal attacks and the concomitant need for nitroglycerin for relief of symptoms, and improves exercise capacity in patients with stable angina pectoris.