An autosomal recessive mutation, characterized by an absence of sebaceous glands, and by hyperkeratosis, alopecia, and single (rather than the usual multiple) hair-follicle units, has occurred spontaneously in the BALB/c strain of mouse. Studies in which reciprocal transplantations of skin were made between normal and mutant mice suggest that some diffusible substance(s) synthesized by normal skin can stimulate hair growth and alleviate the hyperkeratosis characteristic of the skin syndrome.