The circulation of respiratory viruses was investigated comparatively in a group of 24 subjects vaccinated intranasally with the NIVGRIP inactivated influenza vaccine and in 20 unvaccinated controls. The study relied on the detection by immunofluorescence reactions of viral antigens in exfoliated cells present in the nasopharyngeal secretions collected in January, February and March 1984. In January-February the prevalence of influenza, parainfluenza and adenovirus type 5 antigens was considerably lower in vaccinees than in controls. Simultaneous detection of more than two viral antigens in the same subject was more frequent in controls. The data demonstrate that the influenza vaccine administered not only conferred specific protection, but also stimulated the mechanisms of local nonspecific antiviral defence.