Abstract: Apparatus for treating neoplasms in humans and animals comprising a hollow toroidal applicator which resonates at a specific radiofrequency, and which possess electrically conductive walls on which radial radiofrequency currents flow and generate a high density of uninterrupted magnetic flux within the hollow body. A rotatable antenna connected to a source of radiofrequency power is mounted inside the applicator body to couple with the electromagnetic field of the applicator. The body part to be treated is interposed through side apertures or through the space created by removing a segment of the toroid which can have orifices of predetermined cross sectional areas across which a tubular zone of high magnetic flux travels through the interposed tumor and normal tissue to induce more heat in the interposed tumor tissue than in the interposed normal tissue.