AbstractPreviously described immuno-electron microscopic techniques have been unnecessarily complex and often gave variable results with excess background labeling. By refining existing techniques and standardizing fixation and embedding protocols, we have established an improved procedure for the ultrastructural localization of cytoskeletal filament proteins. This procedure, which may also be used for the identification of hormones and viruses, is described and results are illustrated. All antibodies and tissues examined showed an ultrastructural immunoreactivity pattern with a high degree of specificity and minimal background staining. The technique combines the advantages of increased specificity, simplicity and reproducibility, making it suitable for routine laboratory application. (The J Histotechnol13:9, 1990)