Treatment with nisoldipine (2 x 10 mg tablets once daily) and nifedipine (2 x 10 mg capsules three times daily) in patients with severe, but stable effort angina pretreated with atenolol (100 mg once daily in 19 patients and 50 mg once daily in one patient) were compared for their effects on bicycle exercise tolerance and their adverse effects in a randomized 2 x 4 week, double-blind, double-dummy crossover study. All patients had multivessel disease, 16 patients had occlusion of at least one vessel, and eight patients had a history of myocardial infarction. Two patients left the study during the initial nisoldipine period, one because of aggravation of the angina and the other because of suspected allergic reaction. Addition of nifedipine to atenolol treatment significantly improved the variables measured for severity of angina, such as time of exercise until 1 mm and 2 mm ST-segment depression, total exercise time and total workload. In contrast, no such improvement was noted after the addition of nisoldipine to atenolol. However, nisoldipine resulted in a significant prolongation of the time to the initiation of chest discomfort, the maximum heart rate, and the double product. In atenolol-treated patients with severe effort angina pectoris, nifedipine 20 mg tid improved exercise capacity, while nisoldipine 20 mg once daily did not have a similar effect.