The diagnosis of leukemic reticuloendotheliosis may be made with certainty by the cytochemical demonstration of the tartrate-resistant acid phosphatase isoenzyme in the reticuloendothelial cells. Supportive measures such as blood transfusions or antibiotic therapy are helpful in the treatment of this disease. Splenectomy is beneficial in cases with massive splenomegaly and hypersplenism. Four patients in this series so treated have survived for 1, 5, 10, and 14 years, respectively.