ABSTRACT— The distribution of schistosomal antigen, immunoglobulins and complement C3 was studied by IF stain in 26 biopsies of human liver from 21 cases of hepatosplenic and five of intestinal schistosomiasis mansoni. Schistosomal antigen and immunoglobulins, chiefly of the IgG class and in a lesser intensity complement C3, were seen focally as scanty deposits in cells of the sinusoidal wall. They probably correspond to antigen-antibody insoluble large aggregates which are being removed by local cells of the mononuclear phagocyte system. Gamma globulin of the IgG class and antigens were also present in the granuloma around S. mansoni eggs and dead worms in the human liver. During the early phase of the granulomatous reaction the structure was not efficient enough to wall off completely the antigen, which is seen in cells at the center of the granuloma. As the granuloma matures, antigen demonstration becomes restricted to the miracidium, and immunoglobulins are observed mainly at the periphery. The kinetics of the granuloma formation with intralesional antibody presence promote a progressive antigen neutralization.