Neutrophil peroxidase activity was determined before delivery in 46 pregnant women. 36 of these women were also tested on the 1st day and 30 on the 3rd day after delivery. A significant increase in the average values of neutrophil peroxidase activity was found in all parturients as compared with the controls. The highest peroxidase activity was observed before parturition. The possible mechanism of these changes is discussed.