To evaluate the effects of oxytocics on ACTH and Immunoreactive (IR)-beta-endorphin release, concentrations of these hormones in the plasma of 22 women during spontaneous labor, 22 women in labor who had received oxytocin and 19 women in labor who had received PG.F2 alpha at the time of vaginal delivery, were measured. Maternal ACTH and IR-beta-endorphin concentrations were elevated during spontaneous or oxytocics induced/maintained labor and peaked immediately after delivery and decreased two hours later. There were significant correlations between ACTH and IR-beta-endorphin concentrations during spontaneous labor and delivery (r = 0.921, p less than 0.0001), as well as in oxytocin or PG.F2 alpha induced/maintained labor and delivery (r = 0.833, r = 0.916, p less than 0.0001, respectively). The concentrations of ACTH and IR-beta-endorphin during PG-F2 alpha infusion were slightly higher than those seen in the other two types of labor. However, there was no significant difference in the levels of ACTH and IR-beta-endorphin among the three types of labor. Simultaneous maternal and umbilical cord plasma samples were obtained in 25 cases at delivery. However, there was no significant correlation between ACTH or IR-beta-endorphin concentrations in paired samples. These results suggest that 1) IR-beta-endorphin is secreted in parallel with ACTH, into the peripheral blood by the maternal pituitary gland in response to the stress of labor during all types of labor and delivery; 2) there is no significant difference in the response of ACTH and IR-beta-endorphin between spontaneous and oxytocics induced/maintained labor and delivery: 3) ACTH and IR-beta-endorphin in cord blood are not of maternal origin.