Abstract: The skin surface of a patient may be irradiated with the microwaves of a frequency of 250 to 353 MHz (i.e., a wavelength of about 85 to 120 cm.). A conductive metal housing having an open bottom and closed walls on all other sides overlies the skin surface. The interior of the housing carries a pair of opposed slabs of material having a dielectric constant of more than 4 and defining a space therebetween. The microwaves are radiated from a microwave antenna projecting into said space through a wall in the housing, with the antenna being generally parallel to the open bottom. The slabs are of sufficient thickness to provide generally uniform electric and magnetic field intensities throughout the space. During operation, air is blown into the space through an aperture in a wall of the housing to cool the skin with the air passing out of the open bottom.