The authors have reviewed the medical records of 421 sessions of hyperthermia treatments in 73 patients treated between 1987 and 1992 at the University Heights Cancer Center and the Indiana University Medical Center in Indianapolis, Ind. Temperatures attained during the course of therapy on each patient have been averaged and the results were evaluated for complete, partial, or no response. All patients had previously failed conventional radiation therapy, chemotherapy and surgery. Responses were defined as: (1) Complete response-lesions that completely disappeared during treatment and the response was sustained for a minimum of 6 months. (2) Partial response-lesions that underwent a reduction in size of greater than 50%. (3) No response-less than 50% reduction in tumor size during the course of treatment. Response varied somewhat according to histology and anatomical site of treatment; however, complete response was achieved in 45%, partial response in 48% (for an overall response of 93%), and no response in 7% of the patients. The response achieved varied with temperature attained and a minimum temperature of 40 degrees C for 40 min produced the greatest number of responses. Response to hyperthermia was directly related to the temperature achieved and the length of time the temperature was applied.