Hitherto there has been no pre-eminently satisfactory method of applying diathermy to an irregular surface such as the face, the elbow or the ankle. The difficulty has been to obtain a sufficiently close and even fit of the electrode over the surface; the result of irregular contact is that certain spots are overheated. The following technique arose out of that which I developed for intra-oral treatment.The electrode for external use consists of a rigid insulated sheet of vulcanite or bakelite roughly moulded to form a casing over the area to be treated. A shape for a special part is shown in Fig. 1. It is held in place by means of rubber bands attached to studs embedded in the material in suitable places (Fig. 2). The base is totally lined on the tissue side with metal foil, which is connected to an external terminal. When required for use, the metal surface of the electrode is thickly coated with Diatol I, a plastic conducting material (Fig. 3).