In 1975, we initiated a clinical study using multiple cutaneous lesions as the model system to determine whether hyperthermia alone or as an adjuvant to radiation evokes better tumor control than that achieved with radiation alone. The clinical observations of the heating patterns observed in tumor tissues and the adjacent normal tissues indicate that there was selective heating of superficial cancers in more than 80% of the cases. Using fractionated heat alone, there was a transitory tumor response in 10 of 19 patients. When combined with radiation and heat, the complete response achieved was 78% (42 of 54). Investigations in animal tumors indicate that the importance of the site of growth is related to local tumor control by heat alone. Other studies designed to investigate whether localized hyperthermia alone or with radiation increased tumor metastases were negative.