A survey of serum samples from mammals trapped in Central Ontario showed that many contained antibodies to Toxoplasma gondii. The prevalence of infection as reflected by positive reactions in the Sabin-Feldman Dye Test appeared to be related to the type of diet of each species examined, and specifically, to the proportion of rodents in the diet. Of the fox blood samples tested, 84% were positive. The percentage of positive samples diminished through, coyote, mink, bear, fisher skunk, raccoon, marten and rabbit. Blood samples from squirrel, deer, hare and groundhog were negative.