Chromogranin A (CGA), a large acidic 48-kD protein, costored and coreleased by exocytosis with catecholamines, has been shown to be a precursor of peptides that exert feedback regulatory control on catecholamine secretion. In plasma, CGA levels increase in response to a large-amplitude physical stimulation in adult subjects and may be related to catecholamine levels. Any skin information is not yet available when the sympathoadrenal system is highly active during birth. This activation is strongly related to parturition circumstances such as the mode of delivery. The aim of our study was to determine CGA plasma levels in infants delivered vaginally or by elective cesarean section and to investigate the possible correlation between CGA and catecholamine concentrations. Plasma levels of catecholamines (norepinephrine and epinephrine) and CGA were assessed by HPLC with electrochemical detection and immunoenzymology, respectively. CGA and norepinephrine concentrations were significantly higher (p < 0.0002 and p < 0.02) in infants vaginally born than in the group delivered by elective cesarean section. A significant relationship (p < 0.04) was found between CGA and norepinephrine levels. However, for epinephrine, no significant difference was found between both groups. These results demonstrate the fetus' ability to corelease CGA and norepinephrine massively in response to stress of birth.