The feasibility of detecting herpesvirus DNA in paraffin sections of routinely fixed and processed human necropsy brains by use of the polymerase chain reaction (PCR) was assessed. A 110 bp segment of the thymidine kinase gene of herpes simplex virus type 1 (HSV1) could readily be amplified in sections from the brains of six patients with acute HSV1 encephalitis but not from those of six patients with other neurological diseases, including varicella-zoster encephalitis and herpes simplex virus type 2 encephalitis. Primers suitable for amplifying c-myc were included in the PCRs for assessment of DNA preservation. This was found to be adequate to allow amplification of c-myc DNA in sections from all of the brains studied. The PCR provides a simple and specific means of detecting HSV1 DNA in routinely processed necropsy material.