Regular laboratory and clinical examinations were carried out in 150 patients with acute respiratory diseases and 25 normal subjects from family foci in whom adenovirus antigen was found in the epithelial cells of the nasal mucosa by means of the immunofluorescence test upon admission. By combinations of various laboratory methods adenovirus infection was confirmed in all the subjects under study. In preparations obtained from normal subjects, predominantly nuclear localization of adenovirus antigen was observed. In patients, localization of the antigen varied. Detection of cells with nuclear localization of adenovirus antigen, the regularity of this localization and the duration of this finding suggest latent infection, whereas findings of cells with cytoplasmic localization of the antigen and an increase in the number of such cells in the course of the disease suggest active adenovirus infection.