Octodon degus occurs abundantly in an endemic trichinosis area of Chile. However, Trichinella spiralis, the etiologic agent for trichinosis has not been reported as a natural or laboratory parasite of O. degus. In this study, degus were found to be susceptible to doses of T. spiralis as low as 20 larvae, and there was·a direct relationship between the number of larvae recovered from the degus relative to the size of the infective dose. Adult T. spiralis worms were recovered from the small intestines of the degus from day 9 through day 36 post-infection. The newborn larvae were first observed in the skeletal muscles on the 18th day of post-infection. The fecundity of the female worms ranged from 1 to 160 muscle larvae per ingested larva. Degus were found to harbor as many as 900 larvae per gram of tissue. O. degus showed no immunity to an immunizing dose of T. spiralis, based on the number of larvae recovered from the muscles. Thus, degus are the first mammalian species which failed to develop an immune response to T. spiralis. A minimum dose of 100 trichina larvae was required to elicit clinical signs in O. degus. Within 2 months, degus lost up to 38% of the normal body weight due to trichinosis. T. spiralis larvae in tap water were found viable up to 12 days at 5 C and 20 days at 25 C. T. spiralis could be transmitted through O. degus to Sprague-Dawley rats and vice-versa. Transplacental migration of larvae was not observed in either O. degus or Sprague-Dawley rats. Among the degus, the gestation period ranged from 60 to 75 days and the annual infant mortality rate was 13%. Further information on the development, reproduction, and behavior of degus is presented. / Master of Science