Serum creatine kinase (CK) activity after cold exposure in rats acclimated to cold, hypoxia, or combined factors (both cold and hypoxia) were observed under normoxic [correction of normoxie] and hypoxic condition in order to study the degrees of damage to the tissues. The results showed that resistance to frostbite increased in rats acclimated to cold; resistance to frostbite decreased markedly in rats acclimated to hypoxia, i.e. negative cross-acclimation exists between hypoxia and cold. The changes in serum CK activity in rats exposed to both cold and hypoxia for 4 weeks were essentially the same as those in hypoxia-acclimated rats, and were different significantly from those in cold-acclimated rats. It indicates that the effects of hypoxic exposure were stronger than those of cold exposure, its mechanism remains an area for further study.