Mice immunized with antigens derived from Trichinella spiralis muscle larvae or Hymenolepis nana embryos were found to be protected against the homologous challenge infection. Intraperitoneal route was found the most effective in stimulating protection compared with subcutaneous or intravenous administration. Even a single dose of antigen administered intraperitoneally stimulated a significant protection. The results of our experiments confirm that the route of administration has a noteworthy influence on the effectiveness of the immunization. The possible mechanism involved in rejection of both worms population are discussed.