Adrenocorticotropic hormone (ACTH), beta-lipotropin (beta-LPH) immunoreactivity (IR) and beta-endorphin (beta-EP) immunoreactivity (IR) were measured by high-sensitive radioimmunoassay in maternal and umbilical cord plasma samples which were obtained simultaneously in 12 cases. Mean IR-beta-LPH in maternal (690.1 +/- 138.6 pg/ml, +/- S.E.) and cord venous plasma (1114.8 +/- 94.2 pg/ml) were significantly higher than that of normal adults (93.0 +/- 8.2 pg/ml). Mean IR-beta -EP in maternal (125.8 +/- 24.0 pg/ml) and cord venous plasma (130.6 +/- 20.6 pg/ml) were significantly higher than that of normal adults (6.0 +/- 0.9 pg/ml). There were significant positive correlations between IR-beta-LPH and IR-beta-EP in maternal and cord venous plasma. Mean beta-EP to beta-LPH molar ratio of 0.19 +/- 0.03 in maternal plasma was significantly (p less than 0.05) higher than that of cord venous plasma (0.13 +/- 0.01). There was no significant correlation between the levels of these three hormones in maternal plasma and the levels in cord venous plasma. These data suggest that ACTH, IR-beta-LPH and IR-beta-EP were elevate during labor, delivery responding the stress. Beta-LPH and beta-EP in cord venous plasma were fetal and/or placental origin.