Simple criteria were used to select a low-risk group of patients after acute myocardial infarction. The criteria depended on the presence or absence of diabetes, pulmonary oedema, serious rhythm disorders, and recurrent cardiac pain. Patients in the low-risk category with a suitable home environment were discharged from hospital after five to seven days (mean 6.2 days); they constituted 47% of the 267 hospital survivors over 18 months. Mortality in the selected patients was 2.4% at six weeks and 7% at one year. Most complications preventing early discharge were identified on the first day. Provisional selection for a short hospital stay was made after two days, and 76% of those judged suitable at 48 hours remained free of complications. Early selection of a low-risk category is justifiable and of practical value, though subsequent events will delay discharge for some patients. All patients who died in hospital or within two weeks after infarction had developed overt complications by the end of the fourth day. The results suggest that a policy of hospital discharge after four days would be justifiable for a low-risk group selected by the present criteria.