Ultrasonic systems were developed for the treatment of superficial human tumors, generating local tumor hyperthermia at tumor center temperatures ranging from 43 degrees to 50 degrees. Twenty-eight patients with disease of varying histology were evaluable for response, and demonstrated an overall response rate of 57% with a complete response rate of 18%. In 11 patients who had received definitive radiation therapy to the heat treated area, the response rate was 81%; there were no toxicities other than those noted for the overall study. As temperature was escalated a marked increase was observed both in response rates (from 53% (43-44 degrees C) to 83% (48-50 degrees C) and in duration of response (from 29 to 250 days for the same temperatures). Toxicities were minimal, consisting of superficial blistering in four patients and pain in six patients. Pain was usually associated with tumor involvement in the periostium.