A prospective study has been made of 29 human bite injuries caused by the clenched fist, 27 over M.P. joints and two over P.I.P. joints. All were treated by surgical exploration, within 24 hours in 84% of cases. In 62% the wound had entered the underlying joint and in 58% the bone was injured. Significantly less morbidity was noted in those cases where there was no joint injury (P less than 0.001). Early surgical exploration to identify and to treat the joint injury is recommended.