The Norwegian Multicenter Group Study noted the effect of smoking habits before and after myocardial infarction and their relation to mortality and reinfarction rate after treatment with timolol in patients surviving acute myocardial infarction. The mean follow up period was 17.3 (range 12-33) months. No relation was found between initial smoking habits and risk category after infarction or between initial smoking habits and later outcome. At the time of their first infarct smokers were seven years younger than non-smokers. One moth after infarction nearly 60% of the smokers had stopped smoking completely. A significantly lower incidence of early cardiac death and lower total mortality was found in patients treated with timolol in both those who continued smoking and in the combined non-smoking groups and a significantly lower reinfarction rate among non-smokers. Cessation of smoking alone was associated with a reduced reinfarction rate by 45% but a non-significant reduction in mortality by 26%. It is concluded that treatment with timolol and cessation of smoking have an additive effect in reducing mortality and reinfarction rate after myocardial infarction.