Aminopeptidase activity was measured towards L-alanine and L-leucine naphtylamides in the blood serum obtained from the non-pregnant women and from women during the stages of the physiological delivery. In the same samples the concentration of inter-alpha-trypsin inhibitor (alpha ITI) was measured. The highest aminopeptidase activity was observed in the stage II, and it was statistically significant comparing to the stage I, whereas the statistically significant increase in the alpha ITI concentration was noticed in stage I in primiparae and in stage I in multiparae.