Elevated plasma concentrations of beta-lipotropin (beta-LPH) and beta-endorphin (beta-EP) are present in vaginally delivered babies in the first 24 h of life. To establish if fetal distress or different types of delivery influence the secretion of these peptides in the neonatal period, we studied 16 vaginally delivered newborns (VD), 11 neonates extracted through elective cesarean section (CS) and 8 babies suffering from acute intralabor fetal distress (FD). In all groups of newborns the plasma levels of beta-LPH and beta-EP were measured in arterial and venous cord blood, at 1 and 24 h from delivery. beta-LPH and beta-EP were determined by specific radioimmunoassays after silicic acid extraction and Sephadex G-75 column chromatography. In cord plasma, there were no differences between arterial and venous concentrations of either beta-LPH or beta-EP in any of the groups. In the 1st h after delivery the plasma levels of VD newborns were similar to umbilical cord values (beta-LPH: 19.9 +/- 5.2; beta-EP: 18.1 +/- 2.4), while those of CS (beta-LPH: 30.6 +/- 4.5; beta-EP: 30.1 +/- 5.8) and FD (beta-LPH: 64.9 +/- 11.8; beta-EP: 65.7 +/- 24.4) showed a significant increase. At the 24th h of life the plasma concentrations of both peptides decreased significantly in the three groups, but CS and FD babies showed significantly higher plasma values than VD newborns (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)