The original Norwegian Multicenter Study on Timolol after Myocardial Infarction was a double-blind, randomized study comparing the effect of timolol with that of placebo for up to 33 months after acute myocardial infarction. The initial results showed that the cumulated mortality rate was 39.4 per cent lower among 945 patients randomly assigned to timolol treatment than among 939 patients randomly assigned to placebo (P = 0.0003). After the end of the double-blind period the majority of participating patients in the timolol group continued to receive beta-adrenergic blockade, whereas the majority of placebo-treated patients continued without such blockade. During an extended follow-up of participating patients up to 72 months after randomization, the mortality curves of the two groups continued to rise in parallel. Cumulated mortality rates were 32.3 per cent in the placebo group and 26.4 per cent in the timolol group (P = 0.0028). We conclude that the previously observed early beneficial effect of beta-adrenergic blocking therapy is maintained for at least six years after infarction.