The influence of regular physical exercise on fibrinolysis was studied in two groups of patients after myocardial infarction. The two groups were of similar age and living habits. One of the groups took part in a rehabilitative training programme while the other group did not participate in any sports activities. Several fibrinolytic variables, including plasminogen activator inhibitor (PAI) activity and PAI-1 antigen, were studied before and after an ergometric test performed at three different times: at the end of hospitalization (before beginning the rehabilitation programme), three months and six months after myocardial infarction. Our results indicate that by the sixth month fibrinolytic activity, measured by the tissue plasminogen activator (t-PA) capacity, had decreased significantly (p less than 0.025) in the patients who were not participating in the rehabilitation programme whereas it had increased slightly in the patients involved in the rehabilitation programme in comparison with the initial values. It was also observed that while PAI activity remained constant or decreased slightly in patients after six months in the rehabilitative sports programme, these PAI levels increased significantly in patients who were not in the sports programme. Our results indicate that there was a significant decrease in the fibrinolytic capacity of patients who were not participating in the rehabilitation sports programme, while the patients involved in the rehabilitation programme showed a slight improvement in their fibrinolytic activity.