During the past six years the Los Angeles Wildlife Disease Research Station, U. S. Fish and Wildlife Service, has conducted a careful search for ectoparasites from more than 3,000 domestic rabbits, Oryctolagus cuniculus, that have been brought in for observation. All of these came from rabbitries in California, more than half of them from southern California. Because of hutch construction and approved practices of rabbit husbandry, very few ectoparasites are ever found infesting rabbits raised in commercial rabbitries of southern California. On December 4, 1942, a three-year-old, New Zealand White. male rabbit was presented to the Station by a nearby rabbit breeder for diagnosis and treatment. Approximately three iiioiiths before this animal had been placed in a recently acquired, secondhand rabbit hutch. This hutch was not sterilized or disinfected before being used. The seller of the hutch claimed it had been idle for two months. The first indication of any disease was a fine, powdery, meal-like scruff or dandruff which the owner noted in the fur. This spot was located on the dorsal midline approximately five centimeters behind the shoulder blades. The infested spot was roughly circular in shape and approximately five centimeters in diameter. Much of the under fur in this spot had loosened and fallen out. The guard hairs were less in number than in adjoining areas. A very fine, gray-white, slightly oily scale covered this area. This scale could easily convey to the clinician the impression of the early stages of favus. The skin beneath the scale deposits was red, tender to the touch and slightly eroded. No crusts were formed, neither were there any scratch wounds to indicate the rabbit had attempted to alleviate a local irritation. No other affected areas were found although the body and extremities were carefully examined. Other than the infested area the rabbit appeared normal in every respect. Clinical examinations of the scale, skin scrapings and fur from the affected area failed to demonstrate the presence of any fungi. These same materials did, however, reveal the presence of a mite. It was quite evident that this mite was carrying on its complete life cycle on the body of its host because adults, nymphs, larvae and eggs were found. From this evidence and the following analysis of these mites they undoubtedly represent a group, heretofore unknown to science, of true mammalian ectoparasites. It is concluded here a new genus, of the family CHEYLETIDAE, is necessary to hold this interesting parasite. Family Cheyletidae