In spite of the numerous studies and a growing list of publications concerned with the biochemistry of the white blood cell (WBC), many fundamental problems still remain unsolved. There are a number of factors responsible for this situation, but the two most important ones concern the procurement of leukocytes, and the physical and chemical characteristics of the cells. Several methods for the separation of WBC's from red blood cells (RBC's) and platelets are now available but these do not provide for the isolation of leukocytes of uniform age within the myeloid series, or for the separation of granulocytes from lymphocytes. This is of particular importance in biochemical studies involving the cells of patients with chronic myelocytic leukemia (CML). It has been demonstrated that the concentration of many of the enzymatic and nonenzymatic constituents is different in granulocytes and lymphocytes, and that the levels change as the leukocyte matures. In addition