The polymerase chain reaction (PCR) was used to amplify herpes simplex virus DNA using a single set of primers that amplify both herpes simplex virus I (HSVI) and II (HSVII). The viruses can be differentiated by a single restriction enzyme cleavage. Virus from dilutions of HSV-infected A549 cell suspensions were amplified and the infectivity endpoints of cell culture were compared with the PCR, and with another direct detection method, the enzyme-linked immunosorbent assay (ELISA). The PCR was capable of detecting virus at a 10(-4) dilution for both HSVI and HSVII, when the corresponding TCID50 endpoints were 10(-5.9) and 10(-5.7), respectively. The ELISA detected virus only down to the 10(-1) dilution. The amplification procedure showed the greatest sensitivity when an initial protease digestion was followed by filtration. The PCR may have use in detection of HSV in clinical situations in which a rapid result is desirable.