AbstractThis paper illustrates the utility of the reverse transcriptase (RT) in situ polymerase chain reaction (PCR) technique in determining the specific virus present in paraffin embedded, formalin fixed tissue sections. Four autopsy cases were chosen for this purpose. In each case the patient developed a short illness and died before a definitive diagnosis could be made. Multinucleated cells associated with marked inflammation and degeneration of the lung or liver of each patient were evident. By using RT in situ PCR, it was possible to demonstrate that the different cases represented infections by parvovirus, the measles virus, the respiratory syncytial virus, and the hepatitis C virus, respectively. The latter 3 are RNA viruses that can be difficult to detect by standard in situ hybridization because they are usually present within the infected cells in relatively low copy number. The RT in situ PCR technique allows the rapid and specific determination of a viral infection in paraffin embedded, archival material or in cytology preparations. (The J Histotechnol17:247, 1994)