A multicenter double-blind randomized study was carried out to compare the effect of timolol (10 mg twice daily) with that of placebo in patients surviving acute myocardial infarction. Treatment was started seven to 28 days after infarction in 1884 patients (945 taking timolol, and 939 placebo), who represented 52 per cent of those evaluated for entry; the patients were followed for 12 to 33 months (mean, 17). There were 152 deaths in the placebo group and 98 in the timolol group. When deaths that occurred during treatment or within 28 days of withdrawal were considered, the cumulated sudden-death rate over 33 months was 13.9 per cent in the placebo group and 7.7 per cent in the timolol group--a reduction of 44.6 per cent (P = 0.0001). The cumulated reinfarction rate was 20.1 per cent in the placebo group and 14.4 per cent in the timolol group (P = 0.0006). We conclude that long-term treatment with timolol in patients surviving acute myocardial infarction reduces mortality and the rate of reinfarction.