About 25 years ago Dr J. S. Haldane, Dr A. E. Boycott and Capt. Damant, R.N., in the course of investigations for the British Admiralty, worked out a system of decompression for divers and compressed air workers. This system was adopted by the Admiralty, and by its use compressed air sickness has been practically eliminated entirely amongst naval divers. The system has become known as stage decompression, although in fact stages are not an essential feature of it, though a convenience in practical working. The system has been frequently and fully described. The latest explanation will be found in the last edition, 1935, revised by Haldane and Priestly, of Respiration, by J. S. Haldane (Clarendon Press). Its most essential feature is that the pressure is lowered quickly to approximately half the absolute pressure during decompression, and one of the most important assumptions for working out the decompression tables is that different parts of the body saturate and desaturate at different rates. Enquiries sent out by me during 1934 to the United States, the principal countries of Europe and to Japan indicate, so far as definite information has been received in reply, that stage decompression has been universally adopted for divers, but in no case has it been adopted for caisson and tunnel workers in countries where State regulations already existed, except in a modified form, and I conclude that the reason for this failure to adopt stage decompression is the existence of statutory regulations, either still in force, or only partly modified in accordance with new ideas.