The article is devoted to the current problem of differential diagnosis of diseases of viral etiology in small domestic animals. Viral diseases of dogs and cats are widespread among both high-breed and outbred animals. The spread of diseases is facilitated by an increase in the number of small domestic animals, the popularization of pet keeping, and cross-border operations related to the movement of animals. The possibility of using means and methods of diagnosing adenovirus infection in cattle, tentative diagnosis and differentiation of infectious hepatitis in dogs from plague of carnivores and parvovirus enteritis is being considered. Reducing the timing of diagnosis helps to increase the effectiveness of ongoing therapeutic and antiepizootic measures. The analysis of the place of carnivorous infectious hepatitis in the structure of the incidence of dogs is given. The article describes the research in the field of the possibility of using the established antigenic relationship of representatives of the adenovirus family for the in vivo and posthumous diagnosis of infectious diseases of small pets. The authors proposed a method for performing the production of serological reactions for the diagnosis of infectious hepatitis in dogs using diagnostic tools for adenovirus infection in cattle.