The changes in corticotrophin-releasing hormone (CRH), ACTH and dehydroepiandrosterone (DHEA) in maternal and fetal plasma were estimated in women undergoing spontaneous and oxytocin-induced labour to correlate hormone changes with the mode of parturition. Blood was sampled from a maternal peripheral vein 2 days before labour, during the second stage of labour and on the second postnatal day, and also from umbilical vessels just after delivery. Hormone concentrations were measured by RIA and ELSA methods. The maternal plasma CRH concentration before labour was significantly higher in the group of women delivered spontaneously and declined during the labour through to the second postnatal day. Measured in umbilical vessels, CRH as well as ACTH concentrations were higher in the umbilical vein than artery. The mean maternal plasma ACTH was similar in both groups before delivery, then increased significantly in both groups during the labour, decreasing on the second day after delivery. There were no changes in DHEA concentrations among the groups and at all time points of collection. No correlations between CRH and ACTH or DHEA were observed. Our results suggest that the maternal pituitary can respond to stress factors during delivery but peripheral CRH, probably mainly of placental origin, is not a major modulator of pituitary action.