The protective role of secretory antibodies in the development of adenovirus infection has been established. More severe and prolonged course of adenovirus infection, accompanied by the involvement of the lower respiratory tract in the process, has been noted in patients with low titers of antibodies, or their absence, in secretions (O to 1:4). The presence of secretory antibodies in a titer of 1:8 considerably alleviated the course of the disease. The antibody titer 1:16 (according to the data of the passive hemagglutination test) has proved to be protective for children and adults in adenovirus infection. The results of the determination of antibodies in the secretions of the upper respiratory tract in the passive hemagglutination test may be used for the purposes of prognostication.