The methodology of post-embedding immunocytochemistry commonly employs regimens that are more technically difficult than conventional processing and staining of specimens for transmission electron microscopy. Among these regimens are the preparation of frozen thin sections and embedment in hydrophilic acrylic resins such as Lowicryl and LR White . Cryotechnology, however, requires special equipment and exacting preparation of specimens. Use of water-soluble resins likewise demands special care; for example, embedment in LR White involves titrating the dehydration solutions and maintaining oxygen-free curing conditions (usually in gelatin capsules, making selected orientation of specimens quite difficult). It is commonly supposed that conventional treatments such as exposure to osmium tetroxide and uranyl acetate en bloc, with subsequent embedment in epoxy resins, are detrimental to antigenicity.Uranyl acetate block-staining can actually enhance immunocytocheinical staining of some epitopes . Though osmicated tissues have also been successfully immunostained , it is standard procedure first to treat the thin sections on grid with an oxidizing agent such sodium metaperiodate . We have found that a polyclonal antibody to renin effectively immunostains globular inclusions (granules) in juxtaglomerular (JG) cells of rat kidney. This can be accomplished both in unosmicated tissue embedded in LR White (Fig. 1) or in specimens (either intact kidney or isolated JG cells) that have been osmicated, uranyl acetate block- stained, dehydrated through 100% ethanol, and embedded in Poly/Bed epoxy resin (cured at 60 °C). Thin sections were collected on nickel grids and immunostained with Protein A-gold, without prior oxidation to remove osmium (Fig. 1). There are several distinct advantages of using the latter immunocytochemical procedure. First, tissues can be processed in a routine manner; in addition, specific orientation of specimens can easily be accomplished. Furthermore, curing of the embedment does not have to be carried out at low temperatures or in oxygen-free containers; this is particularly useful when processing cultured cells (Fig. 1).