The effect of hyperthermo-radio-chemotherapy (R+C+H) given as preoperative treatment for carcinomas of the lower gum was examined.Hyperthermia was combined with conventional radio-chemotherapy (R+C) consisting of 22.5Gy of radiation and 110mg of bleomycin. Eighteen patients treated by R+C+H and 18 patients treated by R+C were studied. The mandible, resected at operation, was examined histopathologically.Clinically, 9 patients had a complete response (CR), and 7 had a partial response (PR) in the R+C group. In the R+C+H group, 10 had a CR, and 6 had a PR. The histopathological response to treatment was evaluated according to Shimosato's classification in both soft tissue and bone invaded by tumor in the resected mandible. Eight patients (44.4%) in the R+C group and 7 (38.9%) in the R+C+H group showed Grade DI or IV in soft tissue. Three patients (21.4%) in the R+C group and 9 (69.2%) in the R+C+H group showed Grade IQ or IV in the invaded region. The histological response rate (Grade DI+IV) in the R+C+H group was significantly higher than that in the R+C group (p<0.05). Furthermore, in patients in the R+C+H group who had a CR clinically, tumor cells almost completely disappeared from the region of the mandible invaded by tumor.These results suggest that R+C+H therapy is an effective treatment for carcinomas of the lower gum that involve the mandible.