[en] Mice treated with Cyclophosphamide (Cy) shortly before inoculation of influenza A virus exhibited increased mortality and delayed mean time of death. The extrapulmonary dissemination of the infection was observed more often in Cy-treated animals with the titres of virus in different organs substantially higher than in equally infected immunocompetent controls. Although the humoral antibody response was not impaired in Cy-treated mice, they were more susceptible to challenge with a lethal dose of virus than normal animals. In X-irradiated mice, the increased multiplication of virus in lungs and spread of the infection to other organs was observed, with prolonged persistence of virus in lungs and brains as compared to adequate controls, reminding of previous observation in immunocompromised persons, who died in the course of influenza. (author) 1 fig., 4 tabs., 23 refs