The Timolol Myocardial Infarction Study was a completely randomized program of 1884 survivors of myocardial infarction comparing timolol maleate, 10 mg twice daily, with placebo for the secondary prevention of sudden death and reinfarction. In that study, timolol maleate reduced total mortality (152 placebo vs 98 timolol) and the incidence of first nonfatal reinfarctions (131 placebo vs 90 timolol). This report evaluates the effect of timolol in selected categories--age, sex, infarction site, heart size, transmural infarction, diabetes, smoking, multiple reinfarctions and pulse. These data document two important facts. First, the effects of timolol in the total sample were also seen in different subpopulations, and there were no major subgroups for which this positive effect would not be expected. Second, the consistency of the effects observed with respect to pulse, transmural infarction, age and infarct site are in contrast to some previous studies with practolol, propranolol, and alprenolol. Thus, beta blockers may not be identical with respect to reducing the mortality and morbidity associated with acute myocardial infarction.