Since the schistosomiases constitute a serious health hazard to many populations and may be responsible for cancer, many investigations have been instituted to learn more of the principles of parasitism, dynamics of successful infection and various aspects of the biology of the causative agent, Schistosoma. This laboratory has been engaged in multidisciplinary studies on mammalian schistosomes for a number of years. In the coming year work will continue on characterization of definitive host-parasite systems with attention given to finalization of reports on the golden hamster as a host for members of the Schistosoma haematobium complex and on the S. haematobium-capuchin monkey (Cebus apella) system for investigations in schistosome parasitology and bladder carcinogenesis. Research will be finalized for schistosome homologous immunity in capuchins infected with S. haematobium and for heterologous features of immunity in hamsters and capuchins infected with the benign schistosome, S. rodhaini, and subsequently exposed to cercariae of S. haematobium. Investigations on the biology of two "pedigree" strains of S. haematobium will be determined. In these, an attempt is being made to demonstrate that S. haematobium passaged from man only through nonhuman primates propagates a more vigorous parasite with greater infection potentials than the S. haematobium passaged for many generations through rodent (hamster) hosts.