The activation of macrophage after stimulations (infectious, immunologic, irritative) is the ability of this cell to destroy intracellular bacteria and tumoral cells. Activated macrophage is characterized by morphological, biological and immunological properties and by its phagocytosis ability. The activation of macrophage can explain most of the signs encountered in several diseases: familial hemophagocytic lymphoreticulosis, accelerated phases of some immunodeficiencies but also protection of the organism against infectious diseases, immunological tolerance and antitumoral immunity.