The detection of specific RNA species in wax-embedded tissue sections using the polymerase chain reaction (PCR) means that gene expression can be studied and RNA viruses detected in stored histological tissue samples. This technique potentially allows the distribution of gene expression and viral replication to be studied in finely subdivided tissues. A technique is presented that has been used successfully to detect short RNA target sequences (130-420 bases) from proto-oncogene Abelson, human enteroviruses, and the sheep retrovirus Maedi-Visna virus using RNA PCR in single wax sections (20-30 microns). Various tissues were used which had not been deliberately prepared for this purpose. In a simple procedure hot xylene dewaxing is followed by acid phenol extraction of RNA and RNA PCR.