In contrast to the abundance of reports on chemical analyses of plasma or serum lipids, studies concerning lipids of leukocytes have been few. The purpose of the present study is to establish a method for quantification of various lipid fractions of human blood leukocytes and to define the concentration of the cellular lipids, for reference in future studies on the role of leukocytes in lipid transport. The importance of such studies lies in the possibility that lipid-laden leukocytes in the circulation enter the arterial intima and become tissue foam cells, as has been postulated in the pathogenesis of human and experimental atherosclerosis.