Thirty-six patients with chronic, stable angina pectoris were studied during 2-week treatment periods in which they received, in a randomized double-blind, crossover study, a new calcium entry blocking agent, isradipine, 7.5 mg three times daily or placebo. Antianginal efficacy was determined by treadmill exercise testing carried out 3 and 9 hours after drug administration on the final day of each treatment period. During placebo therapy, treadmill exercise time to the onset of angina (P1) and to the development of moderate angina (P2) was similar at 3 and 9 hours and similar to the placebo run-in period. During isradipine therapy, treadmill exercise time 3 hours after dosing was greater than with placebo therapy (P1 312 +/- 23.0 vs. 267 +/- 19.5 seconds, p less than 0.001; P2 410 +/- 20.2 vs. 355 +/- 18.8 seconds, p less than 0.002). Nine hours after drug administration, the results of exercise testing were similar to placebo.