A method involving the combined use of gramicidin and lysolecithin is described for the rapid and apparently quantitative isolation of morphologically intact leukocytes from circulating blood. The mixture of these two compounds gives rapid and complete lysis of erythrocytes. The use of either gramicidin or of lysolecithin alone in sufficient amount to completely lyse the red cells results in morphological damage to the leukocytes. For some as yet unknown reason, however, the combined use of these two agents in a definite ratio results in cancellation of this leukocyte damaging effect. The cells thus prepared appear to be consistently more intact morphologically than any yet prepared in this laboratory.