Parvovirus infection was confirmed by fluorescent antibody staining of or viral isolation from specimens of small intestine in 181 (17%) of 1,110 dogs necropsied between July 1, 1987 and Dec 31, 1990. Clostridium perfringens was isolated from 74 (69%) of 108 dogs with parvovirus infection from which specimens of jejunum also had been obtained for culture of anaerobic bacteria. Gram-positive bacilli in association with focal to diffuse necrosis of the superficial portions of the villi were observed in histologic sections of specimens of small intestine from 56 (98%) of 57 dogs from which parvovirus and C perfringens had been identified. These findings indicate that C perfringens frequently proliferates in dogs with parvovirus infection.