During the course of experiments examining the immunobiology of corneal transplants, the corneas of athymic, nude mice (nu/nu) were found to contain blood vessels that extended through the entire superficial stroma into the centermost portion of the cornea. The presence of corneal vessels was not related to the immunodeficient condition of the nude mouse since corneas from the severe combined immunodeficiency (SCID) mutant mouse strain were avascular and indistinguishable from corneas obtained from immunocompetent BALB/c mice. Furthermore, Langerhans cells were not found to accompany the blood vessels in the corneas of any of the nude mice examined. Corneal vascularization that was similar to that seen in the nude mouse was found in the cuthymic, hairless mutant mouse strain (SKH1; hr/hr). Although vascularization of the corneal stroma was associated with the heritable loss of hair, the genes responsible for hair loss in these two mutant mouse strains reside on different chromosomes. Understanding the processes involved in either promoting or preventing corneal vascularization may have significant impact in preventing corneal allograft rejection and in controlling inflammatory diseases of the corneal surface. The two mutant mouse strains described here may serve as valuable tools for such investigations.