Concentration of beta-endorphin in relation to the mode of delivery and anesthesia was studied in maternal and umbilical cord plasma in 30 healthy women at term pregnancy. At elective cesarean section under epidural anesthesia, the mean maternal beta-endorphin level rose from 9.8 +/- 2.7 pmol/L (SE) before induction to 15.5 +/- 3.7 pmol/L at the time of delivery (P less than .02). Under general anesthesia the mean beta-endorphin level increased more, from 14.6 +/- 7.2 to 34.4 +/- 7.8 pmol/L (P less than .02), reaching the mean beta-endorphin value of the second stage of normal labor, 39.4 +/- 7.0 pmol/L. In the cord arterial and venous plasma, the mean beta-endorphin value was significantly higher after spontaneous labor (40.9 +/- 11 and 40.1 +/- 9.2 pmol/L, respectively) than at elective cesarean section under epidural (14.3 +/- 1.9 and 12.4 +/- 3.6 pmol/L, respectively) or general anesthesia (11.9 +/- 2.2 and 13.4 +/- 2.2 pmol/L, respectively). Thus cesarean section under general anesthesia proved to be more stressful for the mother than that under epidural anesthesia, when beta-endorphin release is used as the measure of stress. The mode of anesthesia did not seem to influence the plasma beta-endorphin level in the newborn infant. Normal delivery by vaginal route increased the release of beta-endorphin both to the maternal and the fetoplacental circulation.