In the isolation of leukocytes, it is desirable to minimize contamination with erythrocytes and platelets, while retaining a satisfactory yield of viable cells. Viability, however, is difficult to evaluate and is not definable by any one specific functional test. Tunis states that leukocytes lose different functions at varying times, first losing their oxidative metabolism, followed in order by the loss of their phagocytic ability, ameboid activity, brownian movement, resistance to impermeable dyes, and lastly, morphologic appearance. Numerous methods for the isolation of human leukocytes have been developed. These include the use of substances of high molecular weight as a means of inducing formation of rouleaux (e.g., dextran,' fibrinogen, phytohemagglutinin,' and gamma globulin), flotation methods, selective destruction of erythrocytes by means of using dilute acids, and hypotonic solutions. For a review of methods in common use, the reader is referred to Walford. Sedimentation methods with high-molecular