Background: Biogenic amine, adrenaline, noradrenaline, dopamine and 5-hydroxy-tryptamine (5-HT) levels are related to interleukin-6 (IL-6) plasma concentrations and endurance exercise. The aim of our study was to investigate the effect of the mode of delivery on maternal-neonatal IL-6, biogenic amine and their precursor amino acid levels. Methods: Some women with normal pregnancy (n=56) were divided into two groups: group A (n=26) with normal labor and vaginal delivery, and group B (n=30) with scheduled cesarean section. Blood was obtained from the mothers at the beginning of labor and immediately after delivery (pre- vs. post-delivery), as well as from the umbilical cord (CB). Total antioxidant status (TAS) and IL-6 levels were measured with commercial kits, the precursor amino acids, tyrosine and tryptophan with tandem mass spectrometry and the biogenic amine blood levels with HPLC methods, respectively. Results: TAS, IL-6, biogenic amine and their precursor amino acid blood levels were similar in the two groups of mothers pre-delivery. TAS levels were reduced, whereas the amino acids, the catecholamine, 5-HT and IL-6 levels were increased post-delivery and in the CB of group A and unaltered in group B at the same time of the study. Conclusions: During a vaginal delivery process, the low TAS, the increased levels of the studied amino acids, the catecholamines, 5-HT and IL-6 may be due to the activation of the neuroendocrine system and the participation of skeletal and uterine muscles. The mode of delivery may be taken into account when IL-6 plasma levels are evaluated as an anti-inflammatory index perinatally. Clin Chem Lab Med 2008;46:1624–30.