The MONICA Haute-Garonne Centre studied the incidence of myocardial infarction and death from coronary heart disease in 1,762 cases between 1985 and 1989. Changes in treatment were analysed in the subgroup of 416 patients admitted to hospital for myocardial infarction in 1986 and in 1989. The incidence of myocardial infarction decreased in men from 218.4 to 183.9 per 100,000 inhabitants (p < 0.01) and decreased nonsignificantly in women from 19.3 to 23.2 per 100,000 inhabitants (NS). The decreased incidence of myocardial infarction in men was exclusively due to a decrease by one-third of the incidence of infarction in patients with diagnosed coronary heart disease. Although the community mortality remained stable, the hospital mortality decreased by one half in man between 1985 and 1989 (21% versus 10%, respectively, p < 0.001). Between 1986 and 1989, the prescription of acetylsalicylic acid during the acute phase increased threefold (26.4% versus 72.9%, p < 0.001) and increased fivefold when coprescribed with fibrinolytics. Similarly, the prescription of aspirin on discharge from hospital doubled (from 32.6% to 69.5%, p < 0.001). The dosage of aspirin decreased from 500 mg or more per day in 1986 to a daily dose of approximately 250 mg in 1989. Lysine acetylsalicylate was the form most widely prescribed. In this population, patients treated by antithrombotics (aspirin or fibrinolytics) had a more favourable prognosis than patients not receiving any of these treatments. The changes observed in this study population are in line with the published results of therapeutic trials on antithrombotics in the acute phase of myocardial infarction and in the postinfarction phase (GISSI2, ISIS2).