Viral DNA stored for extended periods can be amplified by PCR. However, it is unknown whether stored specimens give accurate quantitative results by newer real-time PCR techniques. We therefore compared herpes simplex virus DNA levels in specimens before and after 16 months of storage. The levels of viral DNA remained stable whether the DNA was stored as purified DNA or unextracted DNA in a whole specimen.The PCR has proved invaluable in the diagnosis and management of viral diseases by allowing the amplification of minute quantities of viral nucleic acid in patient specimens. PCR has also been instrumental in research on these diseases. A recent advance in PCR technology has been the development of so-called real-time PCR systems. These homogeneous assays allow the rapid detection of the PCR product with a minimum of specimen handling and provide quantitative measurements of the viral nucleic acid in patient specimens.For research purposes, PCR is often performed with specimens which have been stored for an extended period. Even in prospective studies, specimens are often stored for months or years and are then batched for a large PCR run. In addition to using laboratory resources more efficiently, such batching eliminates run-to-run variations in a PCR which might complicate interpretation of results. Several groups have reported that viral DNA stored for extended periods generally remains positive by qualitative PCR (2, 3, 8). However, it has not been investigated whether standard storage conditions retain the quantitative information on the viral DNA present in patient specimens. If storage reduces viral DNA levels as determined by PCR, it would complicate the design of studies which use archived or batched specimens. To address this issue, we performed quantitative PCR for herpes simplex virus (HSV) DNA with a large series of fresh specimens and again after 16 months of storage. Our results demonstrate that the quantitative information for stored specimens is well retained when HSV DNA levels are determined by real-time PCR.