The dynamics of secretory antibody formation, the duration of secretory antibody preservation, and changes in the concentration of secretory antibodies to antigens other than influenza virus were studied in 64 patients with influenza A, 105 patients with influenza B, and 23 persons who had had influenza A. Severe forms of influenza A were accompanied by antibody accumulation in sera and nasal secretions; in some cases of mild forms of this infection, this process was limited by the humoral immunity system. In the first days of severe forms, transudation of antibodies from sera to nasal secretions was noted. Secretory antibodies to influenza A virus were preserved at titers of greater than or equal to 1:4 for four to eight months in persons with mild forms of the disease and for more than eight months in those with severe influenza A complicated with pneumonia. Decreases in the titer of antibodies to agents other than influenza A virus, including influenza B virus, respiratory syncytial virus, adenovirus, and staphylococcus toxin, were demonstrated in association with rises in titers of antibody to influenza A virus. Among patients with influenza B, who were infected with a new influenza virus variant, the formation of circulating antibodies was more intensely stimulated than was the formation of secretory antibodies. No correlation between the level of IgA and the antibody titer in nasal secretions was found.