Electron microautoradiography, a technique for observing distribution of radioisotopes in metals by electron microscopy, is described. The specimen is prepared, and a carbon layer is deposited on it. A silver halide emulsion is spread over the carbon as a monolayer. The emulsion is developed while still on the specimen, separated by immersion in acid, picked up on a grid, and examined by electron microscopy. To minimize hydrogen diffusion from the specimen during exposure, specimens should be kept at liquid nitrogen temperatures. Examples of use of this technique for studying hydrogen distribution in AISI 4340 steel during cathodic charging, delayed hydrogen cracking, and stress corrosion are given.