The authors compared the serum DHAS and cortisol level in 53 vaginal deliveries with those of 21 caesarean sections prior to the onset of labour at the 28th to 36th weeks. They also compared 18 vaginal deliveries with 16 elective caesarean sections at the 40th week. The serum hormone concentrations were measured in the maternal vein, the umbilical vein and the umbilical artery. The results indicate that the serum DHAS and cortisol level was higher after vaginal delivery than after caesarean section in the maternal vein, umbilical vein and umbilical artery at the 28th to 36th and also at the 40th week. The authors suggest that, although the role of the fetal adrenal cortex is not so definitive as in the case of some species in the onset of labour, it may be presumed that the increase in adrenal cortical activity cannot be explained exclusively by maternal stress.