Since 1991, herpesvirus infections have been reported among larvae and juveniles of various bivalves. Most of the studies focused on detection of viral infections of economically important species. However, the persistence of bivalve herpesviruses; in the marine environment is poorly documented. The present study concerns the role of seawater parameters in Ostreid Herpesvirus I (OsHV-1) detection by polymerase chain reaction (PCR). Viral DNA extracted from purified particles or virions present in infected oyster larvae were detected by PCR after storage in different media at different temperatures. The lowest detection threshold was found using distilled water or Tris EDTA buffer. In seawater, the threshold was higher. The use of sterile media permitted detection of viral DNA stored over a longer period. Storage temperature also had a significant influence on detection, with lower temperatures promoting DNA detection over a longer period. In summary, water parameters such as temperature influenced detection of OsHV-1 DNA by PCR. However, the PCR technique may also be successfully applied to samples in natural seawater. Indeed, the PCR technique permitted detection of naked viral DNA at 100 ng l(-1) in seawater in bioassays.