Intestinal lesions caused by a calf diarrheal reovirus-like agent were studied by scanning electron microscopy, light microscopy, and immunofluorescent microscopy in 2 gnotobiotic calves inoculated per orum. The calves were euthanatized 6 hours after the onset of diarrhea. Villi in the cranial and middle parts of the small intestine appeared shortened. In these areas, the epithelium was composed of low columnar and cuboidal cells. Villi in the caudal part of the small intestine were short. By scanning electron microscopy, the villous epithelium in the caudal part of the small intestine of both calves and the ridge epithelium in the ansa spiralis coli of 1 calf were composed of various sized cells which gave the surfaces an irregular appearance. The amount of mucopolysaccharide in the colonic epithelial cells of both calves was greatly reduced. The combined use of scanning electron and light microscopic techniques enabled obtaining a more accurate description of the intestinal lesions than either technique alone.