Clostridial myonecrosis is described for the first time in a black bear (Ursus americanus). This fatal condition appeared within three days following immobilization with parenterally administered promazine hydrochloride and phencyclidine hydrochloride. Clostridial myonecrosis may be responsible for other unexplained deaths of animals following recovery from immobilizing drugs. Administration of prophylactic antibiotics to immobilized animals might be considered.