Enzyme immunoassay system has been developed for measuring the titers of secretory IgA in secretion from the upper respiratory airways (SURA). Russian ingredients are used. The conjugate includes monoclonal antibodies to heavy chains of human secretory IgA. The sensitivity and specificity of the kit was tested with SURA of normal subjects and patients with influenza. The initial level of specific secretory IgA antibodies detected by the kit clearly correlated with defense from natural influenza infection. The protective concentrations of the antibodies corresponded to at least 1:64 dilutions. The titers of serum and secretory antibodies in convalescents after influenza A or B were virtually the same. The level of secretory antibodies dropped sooner than that of serum antibodies.