Viral hemorrhagic septicemia virus (VHSV) is the etiological agent of viral hemorrhagic septicemia (VHS), which is one of the most serious viral diseases affecting cultured olive flounder (Paralichthys olivaceus) in Korea. Mortality due to VHSV infection in olive flounder appears in the cold-water season at 8 to 15˚C. Among factors contributing to the onset of VHS epizootics in olive flounder, the water temperature plays essential role in regulation of VHS outbreaks. In order to estimate the VHSV infectivity and distribution, we performed cell culture and qRT-PCR in flounder target organ after VHSV infection. VHSV titration and distribution were similar between spleen and kidney. The different differential expression kinetics of four immune-related genes in spleen and kidney were observed in this study. Perforin was immediately up-regulated and then continuously expressed within 48h in both of spleen and kidney. Mx gene showed the highest immune-related gene expression in this study. IL-8 and ISG-15 were expressed in spleen. It was peaked at 15h and then gradually decreased, whereas these were not relatively expressed in kidney. Our study showed that the immune response in host was immediately activated, further study needs to interpret the interaction between host and pathogen f...