indicating tBDv replication in the brain of the affected horses (de la Torre anid others 1996, Gonzalez-Dunia and others 1997, Sauder and de la Torre 1998). Some investigations have detected BDV antibodies and a BI)v nucleic acid sequence in sera and PB\MCs from clinically, healthy horses through the use of immunoblotting or Pc K techniques (Nakamura and others 1995, Bahmani and others 1996). They demonstrated seropositivity against ml)\ protein and Box RNA signlals by PCR in healthy horses, anid suggested that BDV is more widespread than has been thought in healthv horses worldwide, as wvell as in Japan (Nakamura and others 1995). Otherwvorkers demonstrated BD\ RNA-pSitive signals by Pc onlyr in restricted regions of the brainis from horses wvith locomotor disease (Hagiwvara and others 1997). A higher prevalence of B\' infection in human blood donors liv ing near thoroughbred horse farms supports the possibilitv that iov may be horizontally transmitted, at least in part, from infected horses to human beings (Takahashi and otlhers 1997). [hus, Borna disease may be considered as a possible zoonotic disease that has spread worldwide, from an enrzootic disease of horses in Germany (Durrwald and Ludwvig 1997). This is the first report describing clinical Borna disease in horses in Japan. The numbers of horses imported from abroad including from endemic areas of Borna disease, atnd the numbers of racing horses travelling around the world are on the increase. Such a situatioin mav enhance the risk of Borna disease occurring in many countries, including Japan.