Thirty-three patients with chronic osteomyelitis of the femur following open retrograde Küntscher intramedullary nailing of the femur were studied to determine possible reasons for the development of infection. In 32 patients the indication for the operation was a closed fracture of the shaft of the femur (recent or malunited) and in one it was to shorten the femur. In 6 patients (18·2%) there was evidence of skin, urinary and upper respiratory tract infection. In 14 patients (42·4%) it was felt that potential infection was present in poor skin overlying the fracture and unhealed laparotomy wounds. Four patients were under the age of 15 years. The operating theatres lacked facilities for room-air exchange, for provision of filtered air or for modern body-exhaust systems. Twenty-two (66·7%) operations were performed by surgeons under training.