A study was made in five cases of Wiskott-Aldrich syndrome (WAS), ranged in the age from seven months to twenty years. Various hemopoietic progenitors were analyzed by using in vitro clonal culture method in the bone marrow of one patient and in the peripheral blood of five patients. We have demonstrated the presence of normal to slightly elevated numbers of megakaryocytic progenitors in all of the patients' blood and bone marrow. Although one patient had decreased megakaryocytes in the bone marrow, simultaneous examination of megakaryocytic progenitors in the blood and bone marrow revealed normal or higher than normal value. Eosinophilic colonies from the peripheral blood significantly increased in three patients with eosinophilia, while those were within normal range in two patients without eosinophilia. The colonies of the other lineages were found to be grown well. No apparent morphological difference was observed in the constituent cells of the clonies between the patients and normal subjects. These resutlts indicate that the hemopoietic progenitors in the patients with WAS possess normal proliferative and maturational capacity. It is also suggested that eosinophilia in the patients with WAS may be caused by increment of eosinophilic progenitors.
