Concentrations of IgG is maternal serum and in umbilical cord blood were determined in two groups of patients: one group had spontaneous vaginal deliveries and the other elective Caesarean sections. Mean umbilical cord serum IgG after vaginal delivery was significantly higher than the mean value after elective Caesarean section. The difference between the maternal serum IgG livel and the umbilical cord serum IgG level increased as did the duration of labour.