ABSTRACT Crude antigen prepared from adult Gigantobilharzia worms was used - for the first time - to immunize Balb/c mice against challenge infection with Schistosoma mansoni. Results of immunization were estimated by appearance of eggs in stool, antibodies in serum by Indirect Haemagglutination Test, counting the number of eggs and adults in liver and intestinal veins and tissues, estimation of the number and size of granulomas in the liver as well as description of adults deformities by ordinary and scanning electron microscopes. Obvious reduction in all these parameters was recorded in immunized mice. Further studies were recommended through the use of purified bird schistosomes antigens.