A relation between per cent of the hemoglobin that is of the fetal type at birth and gestational age has been demonstrated. Data are presented which show that, after 34 weeks gestation, the per cent fetal hemoglobin drops approximately 3 to 4% per week prenatally. This is similar to the postnatal weekly decrease reported by other authors. Intrauterine hypoxia, particularly of the sort associated with postmaturity, was not found to be associated with an increase in per cent fetal hemoglobin and probably not associated with an increase in total hemoglobin in the body. On the basis of reticulocyte counts and clinical examination and in the absence of studies of blood volume, it is suggested that the increased total concentrations of hemoglobin observed in the postmature infant with prenatal hypoxia are possibly the result of hemoconcentration rather than erythropoietic response to lack of oxygen.