Mitotic figures are always discoverable in the cells of the bone marrow, lymph glands, spleen and other tissues of patients dying of acute leukemia. The occurrence of mitotic leukoblasts in the peripheral blood of patients suffering from leukemia is either rare or the mitotic white cells have been falsely interpreted as mitotic erythroblasts. Dock1 studied mitotic leukoblasts and erythroblasts and reviewed an extensive but uncertain literature. Tannhauser2 described mitotic leukoblasts in the peripheral blood of a patient with acute leukemia. Bowcock and Bishop3 reported a case of acute leukemia in which the peripheral blood frequently contained a type of mitotic