Effect of beta-carotene on experimental infection with A/Aichi/2/68 (H3B2) is studied in mice infected in an infective dose of 5-10 LD50. The drug notably decreased the mortality in experimental group in comparison with the control. Disease symptoms were less expressed and deaths observed later (7 days vs. 4 in the control) in mice treated with beta-carotene. Histological analysis of the lungs showed smaller foci of lesions. Metaplastic changes in the bronchial epithelium, typical of late terms of infection, were far less expressed in these animals. On the other hand, virus titers decreased negligibly in comparison with the control group. Electron-microscopic study of the effect of beta-carotene on virus population showed that virus replication in chick embryos in the presence of beta-carotene led to an increase in the percentage of filamentous and giant polygenome virus particles. The data indicate that beta-carotene is a promising drug for prevention and treatment of influenza.