(Em) have been produced by feeding eggs to several strains and species of laboratory rodents (Rausch, 1954; Mankau, 1956, 1957; Vogel and Schumacher, 1957; Sadun et al, 1957; Yamashita et al, 1958 Lubinsky, 1960a, b). Sadun et al (1957), in our laboratory, reported that the CFW strain of albino mouse fed eggs of Em was resistant to infection, but that the cotton rat, Sigmodon hespidus, was very susceptible. Infection in cotton rats develops rapidly (in 1 to 2 months) and eventually kills the host. Cysts grow to 1 cm in diameter and emanate first from liver and lung tissue, and finally invade other viscera until the organs are compressed or displaced. Host and parasite tissue are so intimately mingled that complete separation is impossible. In continuing our search for a practical mIethod of obtaining Em cyst material as free from host tissue as possible and also for a practical technique of maintaining the parasite in the laboratory without the use of eggs of Em, experiments were initiated to produce infections by means of intraperitoneal inoculation of viable cyst cells frorll animal to animal. The transplantation of Echinococcus grandnlosis (Eg) and Em cyst tissue via intraperitoneal inoculation has recently been reported by Yamashita, Ohbayashi and Konno (1957); Schwabe, Schinozi and Kilejian (1959), and Lubinsky (1960a, b). Continued attempts to render our CFW mice susceptible to infection by treatment with cortisone either before or simultaneously with oral feeding of eggs rXesulted in production of only very limited parasitic material; however, feeding of eggs to gerbils resulted in fairly good infections, suggesting that these rodents mlight be suitable animals for further investigation. Using infected gerbils and cotton rats as the sources of viable cyst tissue, intraperitoneal infections in gerbils