Methemoglobin formation in the presence of acetylphenyl hydrazine occurs faster in red cells from cord blood than in normal adult erythrocytes. Under the same conditions, the rate of disappearance of glutathione is slower in cord blood erythrocytes. The mean NADH-methemoglobin reductase activity of cord blood red cells is less than half of the adult value. The results point to a potential danger in the administration of oxidant drugs to expectant mothers or new-born infants.