Red cell antioxidant enzymes have been recently studied in malignant lymphomas and the results are controversial. Hairy cell leukemia is a rare chronic lymphoproliferative disorder originating probably in a pluripotent stem cell. In the present study, glutathione peroxidase (Gpx), reduced glutathione (GSH), superoxide dismutase (SOD), and catalase were measured in a homogeneous group of patients with untreated hairy cell leukemia and normal controls. Glutathione peroxidase, catalase and SOD activities were significantly lower in patients than in normals. GSH was not significantly different in patients compared to controls. There was no correlation between Gpx, GSH, SOD, and catalase and hemoglobin; reticulocytes, leukocytes, hairy cells, platelets number or splenomegaly. Taken together these data suggest a decreased activity of red cell antioxidant enzymes in hairy cell leukemia and support a pluripotent stem cell defect of these abnormalities.4399-102