Abstract
In 5 different mouse strains, we observed alopecic lesions most commonly in male breeding animals kept with C57BL females. Alopecic areas were located most frequently on the head, but were also found over the shoulders, the back and the pelvic regions. Observations gained through time-lapse photography indicate the cause is a slight increase in self-grooming and a dramatic increase in allogrooming by their female partners. The increased frequency of lesions of males kept with C57BL females suggests that the increased grooming activity may be genetically determined.