A brief description is given of the methods that were employed initially for the location of leaks in cables and accessories. These include the use of amyl mercaptan, the oxygen-sandwich method and the use of heat-flow coils. This is followed by some details of the tests now in general use, including fall-of-pressure and direction-of-flow tests and the use of a halogen tracer gas. The last named is of major importance at present and descriptions of the methods of injection and detection are given. The practical problems associated with this method are also discussed.The paper closes with a brief account of some experimental work that has been carried out with radioactive isotopes.