Abstract Between 1965 and 1967 splenectomy was performed on 21 Watuts and 5 other New Guineans to relieve persistent incapacitating symptoms of tropical splenomegaly syndrome. There were 3 operative deaths. Post-operatively abolition of the splenic red cell pool, correction of the shortened red cell survival time and reduction in plasma volume occurred, leading to a mean rise in haemoglobin concentration of 3·7 g./100 ml. Neutropenia and thrombocytopenia were also corrected. There was a rapid post-operative fall in serum IgG and IgM concentrations, and a prolonged reduction in intravascular pools of both immunoglobulin fractions. The 18 Watuts discharged from hospital and followed for from 41 to 74 months have had significant symptomatic relief, although 7 have died following short illnesses; this mortality rate (36%) is substantially less than that of a comparable group of Watuts not subjected to splenectomy.