Abstract White spot disease (WSD), resulting in more than 90% mortality of aquacultured penaeid shrimp, has been reported off the southern and western coasts of Korea since 1993. The pafuogen of WSD has been identified as being a virion wifu an envelope around a central nucleocapsid, and with an average size of 167 nm in diameter and 375 nm in length. In the present study, an in situ hybridization technique was developed as a rapid. sensitive, and specific diagnostic assay for the WSD viros infection in shrimp. Furthermore. the pathological changes ofWSD, in shrimp experimentally infected with WSD viroses. were investigated. Using a biotinylated 643 bp probe obtained from a peR using primers specific to the rod-shaped virus of Penaeus japonicus (RV-PJ), positive signals were detected in both naturally and experimentally infected shrimps. The in situ hybridization revealed positive reactions in the nuclei of the stromal matrix cells in the lymphoid organ, epithelia of the gills, foregut. epidermis, and hematopoietic cells of the interstitial tissues, suggesting the presence of WSD virus. Tills result indicates that the in situ hybridization method can be useful for a rapid and sensitive detection of WSD viruses in shrimp.shrimp.