We studied the influence of social and personal characteristics on prognosis among 1739 male survivors of myocardial infarction who had been monitored for one hour at a standard examination and subsequently followed for mortality. Over a three-year period men with little education (eight years of schooling or less) who had complex ventricular premature beats in the monitoring hour had over three times the risk of sudden coronary death found among better educated men with the same arrhythmia (cumulative mortality of 33 per cent and 9 per cent, respectively). No such differential appeared in the absence of complex ventricular premature beats. Neither risk factors for incidence of coronary heart disease nor clinical characteristics affecting prognosis accounted for the differences observed. There was no relation between education level and risk of recurrent infarction.