Outbreaks of a disease causing serious losses among populations of cultured penaeid shrimp, including Penaeus monodon, P. japonicus, and P. penicillatus, in Taiwan are characterized by obvious white spots on the carapace, appendages and the inside surface of the body. For this reason, we propose the name 'white spot syndrome' (WSS). Healthy juvenile kuruma shrimp P. japonicus were exposed by immersion to epidermal filtrate from diseased P. japonicus and P. monodon which exhibited marked white spot signs. These experimentally infected shrimp resembled the spontaneously infected ones. Cumulative mortalities reached 100% within 5 to 7 d and were significantly affected by catching and temperature stress. A non-occluded rod-shaped viral particle was found by electron microscopy in the epidermis of both spontaneously and experimentally infected kuruma shrimp. Virions were enveloped, 330 plus or minus 20 nm in length and 87 plus or minus 7 nm in diameter. The close resemblance in external signs and viral morphology between spontaneously diseased and experimentally infected shrimp indicated that the rod-shaped virus may be the main causative agent of the disease characterized by white spot syndrome in Taiwan.