Using tissue from suckling mice infected with Dengue virus, the following improved method for detecting Dengue viral RNA in tissue sections was devised. Reverse transcription of the viral RNA to DNA was followed by the in situ polymerase chain reaction to amplify the viral nucleic acid. This was followed by DNA hybridization with an alkaline phosphatase-labelled probe. The enzyme was then reacted with Fast red and counterstained with hematoxylin. Viral nucleic acid was readily demonstrated within glial cells and macrophages in brains of animals infected with two different serotypes of Dengue.