There is a convincing biological rationale for combining hyperthermia with radiation. Clinical data suggests that adjuvant hyperthermia improves the efficacy of radiation therapy when adequate hyperthermia is delivered. A major stumbling block is the technical difficulty of delivering adequate hyperthermia to all but small, superficial tumors or interstitially implanted tumors. Efforts are being made toward improving hyperthermia technology and treatment techniques. Only after adequate equipment becomes more widely available and quality assurance mechanisms are in place can the true role of hyperthermia be defined.