The separation, characterization and functional assay of the inflammatory infiltrate present in the site of the lesion has been useful in the study of many diseases. Histochemical techniques for esterase and acid phosphatase, as well as the Phagocytose test and the Giemsa staining were applied to the study of the spleen-cell population of ten mice. A good characterization of the components of the Phagocytic Mononuclear System and the identification and quantification of the total cell population were obtained.