A controlled study of hematological changes was performed on 14 patients with the Norrbottnian type of Gaucher disease, seven of whom had been splenectomized at least one year before the study. Each patient had two controls matched to age, sex and habitation. Before splenectomy the patients had slight to moderate microcytic, hypochromic anemia which changed after splenectomy to macrocytic, hypochromic anemia. The splenectomized patients had a high percentage of target cells (mean frequency 33%) and a significantly increased hypo-osmotic resistance of the erythrocytes which showed a positive correlation with the number of target cells. Before removal of the spleen the patients had slight leukopenia with a relative increase of mononuclear cells and moderate thrombocytopenia. In the splenectomized patients the thrombocyte count was normal and there was moderate leukocytosis with a persistent relative increase of lymphocytes.