So far autoradiography has mainly been used at the level of light microscopy and the theory of autoradiography was developed for this type of work. Whatever the intended application, the problems involved can be grouped under (a) resolving power, (b) sensitivity, and (c) technique.An autoradiograph is prepared by bringing a specimen containing some radioactive material in contact with a photographic emulsion and storing the preparation in the dark for exposure. During the time of exposure some of the radioactive material will decay and the ionizing radiations emitted will produce latent images in the emulsion. After photographic processing the developed image will appear as an accumulation of silver grains which are seen as round black spots under the light microscope and as filamentous structures in the electron microscope.