Abstract: An improved electrode and method of use are disclosed in connection with hyperthermal treatment of tumors in humans and animals wherein a radio frequency current is caused to flow between a pair of the electrodes and through a body portion containing the tumor. The electrode assembly includes a fluid conduit in thermally conductive relation with an electrically conductive electrode in the assembly as well as jets arranged about the periphery of the conductive electrode for cooling surrounding surface portions of the body during the hyperthermal treatment. The conductive electrode is connected with a circuit for producing the radio frequency current.