A concept of tissue-cell adaptation to hypoxia (hypoxic preconditioning) is raised and its corresponding animal model is introduced. A significantly strengthened tolerance to hypoxia and a protective effect of the brain extracts from the preconditioned animals are presented. Changes in animals' behavior, neuromorphology, neurophysiology, neurochemistry and molecular neurobiology during preconditioning are described. Energy saving, hypometabolism, and cerebral protection in particular are thought to be involved in the development of hypoxic tolerance and tissue-cell protection. The essence and significance of the hypoxic tissue-cell adaptation or preconditioning are discussed in terms of biological evolution and practical implication.