36 Wistar rats were kept in chronic hypoxic hypoxia of 7 vol % of oxygen in 2 experiments over a period of 6 months, other 36 served as controls. Half of the animals of each group received cytidine diphosphate choline (CDP-choline, citicoline, Somazina; CAS 987-78-0) at a dose of 100 mg/kg body weight in the liquid food. Animals in chronic hypoxia without application of CDP-choline developed pathological symptoms and began to die after 19 to 23 weeks in hypoxia. Rats that received CDP-choline developed less prominent pathological symptoms and died later or remained alive until the end of the experiment. Under conditions of extreme hypoxia CDP-choline exhibited a life-prolonging effect.