The mutant hairless mice which were discovered in Henan Me dical University were close bred to increase new laboratory mouse strains. Usin g brother-sister inbreeding with forced heterozygosity, the mice had been bred 2 3 generations. Genetic analysis of mutant character and skin isografting were do ne in the mice which were close bred more than 20 generations. The results indi cated that the mutant mice had reached the norm of inbred strain, And the mutant gene were hybrid. The new segregating inbred strains that carry normal gene and mutant gene were set up.