On April of 2000 and February of 2001, a disease characterized by darkening, ascites and enlargement of the spleen occurred in flounder, Paralichthys olivaceus, farmed near northern and eastern coasts of Korea. Various degree of necrosis including liquefactive-type was observed mainly in hemopoietic tissue of spleen and kindney. Certain tissue such as branchial soft tissue including epithelium showed a similar necrotic findings. But some tissues such as intentine had several necrotic clusters of wandering cells, being possibly leukocytes. Necrotic evidences of blood cells were evident in various tissues including hemopoietic tissues. Necrobiotic bodies were frequently encountered in blood smear preparations. Bullet type-virious were detected in the spleenic cells. Each virion was about 500 nm in diameter and 170nm in length. From these results, this disease was thought to be a rhabdoviral disease.