Partial dearterialization of the spleen is a surgical method aimed at reducing the volume of the spleen whilst preserving its defensive properties against bacterial infections. Four children with thalassaemia major and one with congenital dyserythropoiesis who developed hypersplenism in the course of their disease underwent the operation and were subsequently followed up for periods of 24 to 36 months. The effectiveness of the method was demonstrated by a smaller enlargement of the spleen, a lesser need for transfusions, a longer life of 51 Cr-labelled red cells and more numerous circulating platelets. Surgery was also effective in reducing post-transfusional iron overload, as shown by the decrease and stability of serum ferritin levels in all children subjected to iron chelation. No episode of infection or changes in serum IgM occurred during the follow-up period, and radioisotopic studies of the spleen showed that macrophage function was preserved in the remaining splenic tissue. One child inexplicably developed thrombosis of the splenic vein 1 year after surgery.