Hyperthermia alone in the treatment of recurrences of malignant tumors. Experience with 60 lesions. Localized hyperthermia alone has been used for the treatment of cancer recurrences in which previous conventional therapies have failed. Since 1983 and 1988, 57 patients with 60 lesions have been heated by means of a microwave and radiofrequency system. Treatment protocol provided 45 minutes of heating at the intratumor temperature of at least 42 degrees C, twice a week, for a total number of six, eight, or ten heating sessions. Invasive intratumor thermometry was performed for all lesions. Complete response (CR) was obtained in ten cases (16.6%) and partial response (PR) in 14 (23.4%). Higher rates of CR were observed in the chest wall (38.5%) compared with the head and neck area (11.4%), trunk (10%), and limbs (none). Adenocarcinoma was the most responsive histologic type (40%). Squamous cells carcinoma had 7.7% CR. The only case of undifferentiated carcinoma showed CR; there were none on five sarcomas. Long-term local control (24 months) was approximately 7%. The multivariate analysis showed the statistical significance of the histologic variety (adenocarcinoma versus others, P less than 0.0001). Side effects and complications of the treatment were minimal. 