IN a recent article in NATURE (May 21, p. 941), attention was directed to the widespread interference caused to radio reception by various classes of electrical apparatus. One of the sources of such interference and also one of the most difficult to mitigate is a certain type of electro-medical apparatus used for diathermy treatment. With the view of securing an amelioration of conditions in this field, the Postmaster-General has asked the Minister of Health to direct the attention of local authorities to this matter. Accordingly a circular letter has been issued by the Ministry of Health to all local councils, including welfare and local education authorities (Circular 1695). With this circular was enclosed a memorandum prepared by the Radio Branch of the Post Office on the prevention of interference with radio reception from certain types of electro-medical apparatus. This memorandum has been reprinted from The Hospital, the official organ of the British Hospitals Association. It is to be noted that modern valve-rectified X-ray apparatus is not likely to cause interference ; and the memorandum is primarily concerned with certain diathermy installations working on medium waves, short waves, and ultra-short waves which can only be prevented from causing interference by the addition of an electrical screen or Faraday cage capable of enclosing not only the apparatus but also the patient and the operator. Since no other effective method of prevention has yet been discovered, it seems desirable that, for new hospital buildings or extensions of existing hospitals or other new buildings in which these forms of apparatus are likely to be used, the inclusion of screened rooms should be considered. Attention is directed to the fact that the Radio Branch of the Post Office is prepared to advise on any problem arising and also on the prevention of interference from existing plant.