We studied the influence of elective cesarean section, under general and epidural anesthesia, on natural killer (NK) cell activity in 12 healthy parturients and in their newborns. The results of peripheral blood samples taken from the mothers before anesthesia and from the newborns 3 h after birth served as basal values against which the results of samples drawn on the 1 st and 5th days following delivery were compared. A significant (p < 0.05) decrease in the NK cell activity after surgery was found only in those mothers given general anesthesia. The differences between the studied groups were not, however, significant. NK activity in the peripheral blood samples of the newborns was not significantly different in the general anesthesia and in the epidural group during the follow-up period. The results show that the depression induced by operative stress on the NK cell function of parturients can be, at least partly, prevented by using epidural anesthesia.