ABSTRACT. The effects of a loading dose of pyridoxine (100 mg) given intramuscularly or per os to 24 earlier non-supplemented pregnant women at term was investigated. The in vitro oxygen affinity (P50) and the prolactin level in both maternal and newborn blood was sampled. The blood P50 values were measured by a variant of “mixing method”. Blood prolactin levels were determined by RIA. After pyridoxine administration, the maternal P50 values increased moderately and the newborns' cord blood P50 values increased significantly when compared with the control group's (number of cases 12) values. The decrease of blood oxygen affinity was most pronounced in the supplemented groups in newborns' capillary blood at the age of five days. The pyridoxine supplementation had no effect on the maternal and the newborns' cord blood prolactin level or on the daily amount of breast milk. Pyridoxine supplementation of the mother at labour may influence favourably the oxygen transport function of the newborn's blood and it may be especially advantageous in early postnatal adaptation disturbances of newborns.