Myocardial infarction (MI) is caused by occlusion of coronary artery and insufficient oxygen supply to a certain area of myocardium. Its necrosis appears as a result of MI. The process of tissue repair after MI is very complicated and it is influenced by numerous factors, including growth factors and proteolytic enzymes. The aim of the study was to determine serum transforming growth factor beta (TGF-beta) concentration on day 2 and 7 after MI and to asses the relationship of this growth factor with serum proteolytic activity of collagenase and elastase. In addition, the effect of fibrynolytic treatment on these factors was evaluated. About 100 patients with MI were enrolled to the study. The control group consisted of 50 healthy individuals. We observed that TGF-beta1 concentration correlated positively with collagenase activity on the second day after MI and that it also correlated positively with elastase activity on day 2 and 7 after MI. Moreover, treatment with streptokinase (SK) caused a significant increase of TGF-beta serum concentration. Our data indicate that TGF-beta1 may be one of the factors involved in tissue repair process after MI. Its effect seems to be mediated by collagenase and elastase and may change with the time that elapsed after MI.