Unoccupied beaver (Castor canadensis) sites in New York State were for two years experimentally scented with a mixture of beaver castoreum and anal gland secretion. These sites were colonized less often than unscented control sites. The beaver is the first mammal to have been shown experimentally to use intraspecific odor cues when settling in vacant habitat. Territorial pheromones may be useful as repellents for beaver or other rodents.