Borna disease is a rare but severe neurological disease of horses and sheep. 
Borna disease virus (BDV) has not been fully characterized because cell-free 
virus has not been isolated. Homogenates of infected brain are infectious both 
for animals and for some cell lines in culture. We report here the partial 
purification and characterization of cell-free BDV from the tissue culture 
supernatant of infected human neuroblastoma SKNSH cells. A single negative 
strand 10-kb RNA was detected in purified virions. Immunoprecipitation analysis 
of the BDV proteins in purified virions shows the presence of the 60-, 38-, 24-, 
and 14-kDa proteins previously identified as BDV-specific proteins in infected 
cells.