A new method for express diagnosis of influenza is described. The method is based on agglutination of antibody-sensitized erythrocytes in the presence of virus contained in nasal washings. Fourteen outbreaks in institutions and 113 patients in appartment foci were examined. The sensitivity and specificity of the proposed test was found to be equal to those of the serological and immunofluorescent methods but to be more advantageous than the latter in the simplicity of its performance and demonstrative results.