The spleens of 124 anatomically normal weight-for-age fetuses and 115 term babies dying between birth and four weeks have been assessed histologically. The mean weight of the spleen shows a steady increase from 27 weeks of gestation up to 42 weeks. There is a weight loss of about 4 gm at the time of birth. The weight of the spleen increases steadily in neonates and, by the fourth week, it reaches the same weight as the full term stillbirth. The amount of lymphatic tissue in the spleen increases steadily in the stillbirths of different gestations and continues, without interruption, at the time of birth and in neonates. The weight loss of the spleen at birth can only be accounted for on the basis of a reduction in the blood lake of the pulp.