Five mule deer fawns (Odocoileus hemionus) ranging in age from 3 to 6 weeks were given sporulated Eimeria mccordocki oocysts orally. Four of the five fawns developed coccidiosis. Initial clinical signs appeared by 8 to 9 days postinoculation and included elevated body temperature and bloody diarrhea. Dehydration and limited emaciation occurred as the disease progressed. The disease was allowed to run its course in one fawn and oocysts were passed in the feces on the 16th day following inoculation. Oocysts passage continued until the 27th day, at which time the animal appeared to be completely recovered. The remaining animals demonstrated all signs of coccidiosis and were euthanized prior to passing oocysts. Intracellular stages of E. mccordocki in these animals were confined to the last 75 to 100 cm of the ileum. The cytoplasm of each infected epithelial cell contained one to five meronts. The intestinal epithelium was inflammatory and contained many necrotic foci.