Rabit mutants with hypotrichosis were found in a colony of Japanese White strain (JW-NIBS) and descendants of the mutants have been successively produced. By genetic analyses, the hypotrichotic condition was inherited by a single autosomal recessive gene, symbolized as htr. The trunk of the htr rabbit did not grow hairs and was covered with a few, fine, soft and short hairs throughout life with the exception of wavy hairs around the nose and extremities. Histologic examination of the skin from htr rabbits revealed thickening of the epidermis, hyperplasia of the sebaceous gland, and dysplastic development of the large guard and small wool hairs. When immunostained with anti AE1 and AE3 antibodies, there were no significant differences in the keratin constituents of the skin between the htr rabbits and age-matched controls. While proliferating cell nuclear antigen (PCNA)-positive cells were numerous in the basal layer of epidermis, external root sheaths, and hair bulbs, apoptotic cells were also increased in the hair bulbs of htr rabbits. There were no significant differences in the number of T and B lymphocytes in the mesenteric lymph nodes between htr and control rabbits.