Oxidized dextran (60 kDa) exerted a pronounced preventive effect in laboratory mice infected with avian influenza subtype H5N1 A/Goose/Krasnoozerskoye/627/05 virus, which manifested in a significant increase in mouse lifetime (by 24.4%) and a decrease in mortality rate (3.3-fold). This was probably related to significant alleviation of pathological changes in the lungs and severity of hemodynamic and inflammatory complications and early fibrosis [corrected].