Monoclonal antibodies can confer resistance to schistosome infections. This has led to identification of several protective antigens. An IgG2a monoclonal antibody designated BRL4 mAb identified a 74-kDa antigen in antigenic extract of Schistosoma mansoni adult worms. The target antigen was localized in gut and tegument. In 3 passive transfer experiments, the BRL4 mAb conferred 51.6, 41.9 and 53.8% protection levels into female Swiss mice. Histopathological examination revealed a marked decrease in number, size, collagen and reticular fibers of the liver granulomas. Further experiments using purified 74-kDa-target antigen as a candidate vaccine will be performed.