Summary Varations in the serial immunoglobulins of 52 children splenectomizedfor a variety of indications were studied and compared with two groups of children, one postoperative and one without operation. The most significant finding was the constant decrease in Ig M in every instance. Our series of splenectomized children seems to confirm the facts noted by other authors. The incidence of serious infections has been clearly significant and is clearly postsplenectomy sepsis. The age of the patients has a great influence on the seriousness of the septic processes, these being more severe on younger children. The influence has also been revealed of the cause which motivated the operation, this corresponding in the first place to thalassemia and in the second place through spherocytosis and pseudohormones. It is evident that the immunologic role of the spleen during early childhood,especially under the age of 5 yr is important. The greatest risk of postsplenectomy sepsis is in the first 2 yr of life. Splenectomy should be delayed until after the age of 5 if clinical circumstances permit. If not, prophylactic chemotherapy should be carried out during the first 18 mo after splenectomy.