From August 1979 until 1988, 26 breast cancer patients with 30 tumours were treated by hyperthermia in combination with radiotherapy. Of the 30 tumours, 11 were locally advanced primary tumours (group 1), six were locally advanced recurrent tumours after operation (group 2) and 13 were locally recurrent tumours after radiotherapy (group 3). The thermal profiles showed that the capability of an RF capacitive heating device is comparatively high for large breast tumours with a volume of more than 100 cm3, and that of a 430 MHz microwave device with a single-lens applicator is excellent for localized tumours. The response rate of group 1 and 2 tumours was excellent, and superior to that of historically controlled tumours that were treated by radiotherapy alone from July 1962 until August 1979. In group 3 the tumour response to thermoradiotherapy was not different from that to radiotherapy, but the possibility of significantly reducing total irradiation dose was indicated. More than one good heating session led to a significantly high local response, and factors having a tendency to influence local response were average minimum tumour temperature, tumour volume, and number of effective heat treatments.