A multicenter clinical trial on the prevention of recurrent myocardial infarction was started in 1970 and continued until March 1977. 946 patients who had survived a myocardial infarction for 30–42 days were randomly allocated in equal proportions to acetylsalicylic acid (ASA, 1.5 g/day) (317 patients), placebo (309 patients) or phenprocoumon treatment (320 patients) and followed to determine the incidence of total mortality, coronary death and nonfatal recurrent myocardial infarction. The ASA and placebo groups were treated double-blind. The observation period for each patient was 2 years. The outcome at 24 months has been established for 231 patients on ASA, for 215 on placebo and for 233 on phenprocoumon treatment. Total mortality was lower in the ASA group (27 patients) than in the placebo (32 patients) and phenprocoumon group (39 patients). These differences are not statistically significant. Coronary deaths (fatal myocardial infarction and sudden death) were 13 in the ASA, 22 in the placebo- and 26 in the phenprocoumon group. This represents a reduction rate of 42.3% in the ASA group compared with placebo (p > 0.1) and of 46.3% in the ASA group compared with phenprocoumon (p < 0.07). Considering male patients alone, the difference regarding coronary death is significant between ASA versus placebo (p < 0.05) and ASA versus phenprocoumon (p < 0.05). Coronary events (coronary death and non-fatal recurrent myocardial infarction) were lower in the ASA group (24 patients) than in the placebo (37 patients) (p < 0.06) or phenprocoumon groups (32 patients). Gastrointestinal discomfort, with or without hermorrhage, was more frequent in the ASA group than in the placebo or phenprocoumon groups. These results, in combination with similar trends reported in other clinical trials with ASA, suggest that ASA treatment is beneficial in patients who have survived a myocardial infarc