Invasive amebiasis caused by Entamoeba histolytica, and particularly amebic liver abscess, is a major public health problem in Mexico and some other countries because of the high incidence and mortality of this disease. This paper first discusses the pathogenic effect of E. histolytica and the defensive response of the host and then reports studies concerning the experimental induction of protective immunity to amebic infection. The pathogenic effect of E. histolytica is probably initiated by a lectin-mediated adhesion of trophozoites to target cells; the adhesion is followed by cytopathic activity and phagocytosis by the ameba. The defensive response is characterized by humoral and cellular immune reactions. Humoral immunity manifests itself by specific circulating antibodies useful in the diagnosis and seroepidemiology of amebiasis. Cellular immunity is shown by several characteristic reactions. Experimental induction of immunoprophylaxis with E. histolytica antigens represents the first stage in the development of a vaccine against E. histolytica for use in humans.