Pasteurella multocida infections of joints and bones generally occur in individuals who have contact with cats or dogs. Osteomyelitis usually follows penetrating trauma such as an animal bite. Septic arthritis tends to occur in patients who have preexisting inflammatory joint disease, especially if a systemic condition which is known to predispose to infection is present. The principles of therapy for septic arthritis or osteomyelitis are no different from those which have been established for other infecting organisms. Although P multocida is susceptible in vitro to penicillin, treatment of septic arthritis with this drug is still associated with a slow therapeutic response.