Seventy patients with far-advanced histologically proven malignancies were treated with a combination of microwave irradiation (433.92 MHz) and ionizing radiation. Of the twenty-one patients who completed the planned course of treatments and are eligible for a minimum of nine-month follow-up, 90% experienced complete relief of symptoms and 10% received partial relief of symptoms. Complete regression of all localized tumor occurred in sixteen of the twenty patients (80%), and nine of the complete responders remain free of disease from nine to fourteen months. It was the opinion of the clinicians involved in this study that the heat administered by the microwave unit potentiated the effects of ionizing radiation over those which would have been seen if radiation were used alone. In view of the fact that all patients in this study had cancers which were previously considered to be refractory to further medical treatment, the marked relief of symptoms and tumor response to combined therapy were encouraging. This preliminary study confirms the impression that the effects of radiation are enhanced by heat and forms the basis for a randomized series involving far-advanced but previously untreated head and neck and gynecological malignancies.