The antianginal effects of 360 mg/day of diltiazem were evaluated, using intrapatient comparisons, in a double/blind, randomized, placebo/controlled trial in 24 young patients (50 +/- 7 years) and in 16 elderly patients (67 +/- 3 years) with stable effort angina. All patients had angiographic documentation of significant coronary artery disease. An open-labelled, randomized, crossover design was employed. For 1 week prior to beginning the study, the patient was on no medication except sublingual nitrates. The study consisted of an initial 2-week single-blind placebo run-in period followed by a 4-week randomized double-blind crossover between diltiazem, 120 mg t.i.d., and placebo. A diary of chest pain and nitroglycerin usage was kept during this period and run-in. Exercise tests were carried out during the run-in period (2 tests) and at the end of the 4-week treatment. After diltiazem 12 of the 24 young patients stopped the exercise test because of angina. A similar number (9/16) of elderly patients stopped the exercise test because of angina. During diltiazem treatment, weekly angina frequency was significantly reduced in the young patients (1.25 +/- 0.67 vs 3.87 +/- 1.19-run-in, 4.08 +/- 1.24-placebo; p less than 0.01) and in the elderly patients (0.87 +/- 0.71 vs 4.06 +/- 1.48-run-in, 4.12 +/- 1.5-placebo; p less than 0.01). Weekly TNT consumption significantly decreased in both groups of patients.(ABSTRACT TRUNCATED AT 250 WORDS)