Hepatic fibrosis and the granulomatous response to eggs of schistosome species pathogenic, for man are studied in mice in relation to parasitologic parameters of infection. Hepatic fibrosis increases in the first weeks after treatment of S. japonicum infection in mice and then remains stable for at least 1 year following therapy. During this period histologic reactions to eggs and dead worms involute and the areas of fibrosis become smaller but denser. Mice vaccinated with paramyosin and BCG showed no significant difference in granuloma sizes or hepatic fibrosis compared to nonvaccinated mice.