Tumors of various types and size in the limbs of rats and rabbits have been destroyed by elevations of temperature to levels near 50 °C Destruction was achieved by diathermy heating at 13.56 MHz; the condenser-field technique was used, and direct-contact electrodes were applied at the site of a tumor. Special features of the heating system provide fo efficient coupling of RF currents to tissues, and for optimizing heating by the currents. Temperatur are continuously monitored via sensors at multiple sites within and without the tumor, which enables a lethal dosage of thermal energy to be delivered to the tumor and to be quantitated in terms of temperature × time. The approach enables a favorable ratio of deep-to-surface heating, which facilitates tumor destruction without damage to normal tissues such as skin and muscle. Initial work indicates that the technique has potential for the selective heating of limb tumors in man.