Changes in the fibrinolytic system of parturient women have so far been only partially documented. Our main questions were whether and how the concentration of tissue plasminogen activator (tPA) and plasminogen activator inhibitors of type 1 (PAI-1) and type 2 (PAI-2) change in the plasma throughout normal labor. The study group consisted of 38 women with normal pregnancy, delivering at term. The concentration of antigens tPA, PAI-1 and PAI-2 in plasma was tested by enzyme-linked immuno-sorbent assay method, and the activity of PAI-1 by plasmin method. Results were analysed statistically. During labor the level of tPA antigen increases over two times: from 9.3 +/- 4.3 ng/ml before labor, to 23.3 +/- 9.6 ng/ml in the second stage of labor. Changes of PAI-1 antigen as well as its activity though noticeable, were not statistically significant. PAI-2 antigen level increased significantly in the third stage (146.3 +/- 58.7 ng/ml before labor, and 212.2 +/- 75.0 ng/ml after placenta expulsion). In summary the more significant change in the fibrinolytic system during labor is an increase of the level of tPA and PAI-2 antigens, but their peaks appear in different stages of labor. The predominance of PAIs over tPA is maintained throughout the whole labor, though on a lower level as can be inferred from the tPA/PAIs ratio.