We observed an incident of interspecific aggression between a male Hoary Bat (Lasiurus cinereus) and a male Silver-haired Bat (Lasionycteris noctivagans). The Silver-haired Bat suffered few external injuries, the most conspicuous of which were a missing lower right canine and small puncture wounds on the left wing membrane. The Hoary Bat experienced much more extensive external injuries, including sub-dermal bleeding on wing and tail membranes and bite marks and tears in both wings. Few published accounts describe physical altercations among bats, but Hoary Bats are frequently involved. Rabies is often implicated as a driving factor in the aggressive interactions. We decided not to euthanize the bat for rabies testing, but encourage others who encounter these types of interactions to have bats tested.