The course of preventive oral treatment with a dihydroquercetin-chitosan composition produced a strong antihypoxic effect under conditions of experimental hypobaric hypoxia (arbitrary altitude 12,000 m). The lactate/pyruvate ratio in composition-receiving rats was much lower than in hypoxic animals (by 83%), but higher than in intact specimens (by 29%). The composition of chitosan and dihydroquercetin also possessed a strong antioxidant activity.