A technique has been developed for the autoradiographic localization of steroids in testes at the light and possibly electron microscope level. During processing of the tissue there is no contact of tissue with water up to the moment of photographic development of the autoradiographs. Tritium labelled steroids have been introduced into the testis through perfusion of the isolated organ. Small tissue samples were rapidly frozen, freeze dried and fixed with osmium vapour. The fixed tissue was embedded in Epon and thin sections could be cut from this material on an ultra-cryotome without the aid of floatation liquids. Results with light microscopic autoradiography indicate the potential of this technique. This procedure which avoids any contact of the tissue with water offers good prospects for autoradiography of steroids and other soluble compounds at the electron microscope level. A comparison is made with other proposed techniques for steroid autoradiography.