beta-lipotrophin (beta-LPH) and beta-endorphin (beta-EP) plasma levels were measured by radioimmunoassay after glass powder extraction and Sephadex G-75 column chromatography in plasma samples from controls (ten healthy males and twenty-six young women in early follicular phase), from eighty-two pregnant women in weeks 9-40 after their last menstrual period, from nine women just after delivery and the cord blood of their neonates, in fifteen mixed cord blood samples and in seven amniotic fluid samples obtained by amniocentesis. No sex differences were found in beta-LPH (120.6 +/- 8.5 pg/ml) or beta-EP (31.1 +/- 2.4 pg/ml) plasma levels or in their molar ratio (1.34 +/- 0.09) (MR). beta-LPH plasma levels increased in early pregnancy (13-16 weeks) (185.0 +/- 27.1 pg/ml) and remained high until weeks 21-24, then declining to levels similar to those of controls. beta-EP plasma levels were significantly depressed in weeks 9-12 (20.7 +/- 5.3 pg/ml), subsequently increasing to a maximum at weeks 36-37 (42.7 +/- 6.8 pg/ml). beta-LPH/beta-EP molar ratio was about double normal in early pregnancy and decreased to normal in the second half. The present data indicate that beta-LPH and beta-EP present different patterns throughout pregnancy and that beta-EP levels increase progressively, reaching the highest concentrations at term. At delivery, both beta-LPH and beta-EP showed maximum values (beta-LPH: 230.2 +/- 20.4 pg/ml; beta-EP: 78.0 +/- 7.4 pg/ml) and a MR of 1.02 +/- 0.10 indicating that stressful situations, such as labour, stimulate a simultaneous rise in beta-LPH and beta-EP plasma levels. Cord blood specimens showed a wide range of values (beta-LPH:75-347 pg/ml; beta-EP: 16-287 pg/ml) with a MR of 1.21 +/- 0.14. Amniotic fluid samples obtained late in the third trimester of pregnancy were characterized by beta-LPH levels of 119.4 +/- 26.4 pg/ml and beta-EP levels of 29.6 +/- 7.5 pg/ml.