Borna disease (BD) is a transmissible, progressive polioencephalomyelitis primarily of horses and sheep. The genomes of two cell-adapted strains of Borna disease virus (BDV), the aetiological agent of BD, have been cloned and sequenced. According to the structural characterization achieved so far, BDV contains a non-segmented negative-sense 8.9 kb single-stranded RNA genome. In this paper we report the expression, purification and intracellular tracing of a novel non-glycosylated BDV-specific protein with a molecular mass of approximately 10 kDa (BDV p10 protein). The successful isolation of the corresponding mRNA from infected cells, amplification of the genetic region by RT-PCR and its efficient expression as a glutathione S-transferase (GST) fusion protein demonstrated that antibodies specific for the BDV p10 protein are induced in infected animals. In addition, we have produced monospecific antisera against the GST-p10 fusion protein in rabbits. This monospecific antiserum recognized the BDV p10 protein in brain cells of naturally and experimentally infected animals as well as in persistently BDV-infected cells. Antibody-mediated affinity-chromatography using the anti-p10 serum could successfully be applied to purify a ca. 10 kDa antigen from infected animal cells to such an extent that glycosylation of this component could be ruled out.