The purpose of the present investigation was to study the feasibility and effect of physical training with maximum intensity in a group of symptomfree male postinfarction patients (n = 15). The patients started training one month after discharge after acute myocardial infarction (AMI). The training was carried out as interval training 2 X 60 min a week during 12 months. During each session there were 5-6 intervals of 6 min's duration, during which the patients exercised with maximum intensity. The results were compared to those of an untrained control group. The groups were randomly selected. Compared to the first exercise test in the third week after AMI the final work capacity of the trained patients was increased by 101%--to 1570 kpm/min (257 W), and that of the control patients by 25%--to 1042 kpm/min. (170 W). (P less than 0.01). The corresponding estimated maximal oxygen consumption was 32 and 48 ml/kg . min. respectively. The study demonstrates that training with maximum intensity is feasible in these patients and that the work capacity, which was obtained, was 30-40% higher than usually found after training of postinfarction patients, when submaximal training intensity has been employed.