The purpose of the research is the development of diagnostic systems for the determination of MPVI (metapneumovirus infection). The main biological properties of field isolates of metapneumovirus (MPV) have been studied. A diagnostic system RIH (reaction of indirect hemagglutination) was developed, with the help of which epizootic monitoring of a new infectious disease of poultry (metapneumovirus infection) among turkeys and chickens in Ukrainian farms was carried out. The results of epizootic monitoring indicate that the developed erythrocyte MPV antigen based on RIH is sensitive and specific and can be used to detect the level of spread of metapneumovirus infection and the intensity of immunity in birds vaccinated against this disease. A diagnostic ELISA test system has been developed and it has been established that this diagnosticum should be used in the practice of veterinary medicine for serological control of metapnomavirus infection. This algorithm can be used not only in veterinary, but also in humane medicine in the development of test systems and the study of post-vaccination immunity to respiratory diseases.