Anaerobic bacteria were isolated from 18 of 28 animals (64%) with osteomyelitis. The bones most commonly infected with anaerobic bacteria were radius and ulna, mandible, and tympanic bulla. Fights or abscesses commonly preceded the osteomyelitis. Seven anaerobic genera were isolated. Mixed infections of anaerobic and aerobic organisms occurred in 16 animals. Staphylococci were isolated in only one such mixed infection, but they were isolated commonly when there were aerobic bacteria only. Staphylococcal infections were often single.