The technique of electron microsco-pic in situ hybridization is applying in situ hybridization at the electron microscopic level. It is mainly used in the ultrastructural localization of the lablled DNA, RNA and RHA in a cell and/or a tissue. In this paper I mainly elaborated its establishment and classification, and the operation procedure of nonradioactive electron microscopic in situ hybridization and some points for attention. In the end I also discussed its application for research.