In this paper, we describe a specific method for ultrastructural detection of RNA. Our method is based in the bromination "in situ" of uridine residues in the RNA, which allows the detection of brominated RNA with specific antibodies against bromo-deoxyuridine. With this method we can achieve high specificity and resolution, and it can be applied to Epon or acrylic resin embedded material. (C) 2005 Published by Elsevier Inc.