Recently, we reported the application of a recombinant chicken IgY monoclonal antibody, Ab3-15, against mammalian prion protein (PrP), for the diagnosis of bovine spongiform encephalopathy in cattle. In this study, we have characterized a soluble, single-chain variable fragment (scFv) form of this antibody, sphAb3-15 using brain homogenates from mice. This sphAb3-15 antibody recognized denatured forms of both PrP(C) and PrP(Sc), and PrP(Sc) after PK-treatment, on Western blotting. In sandwich ELISAs, on dot blots and by immunoprecipitation, sphAb3-15 efficiently bound to PrP from normal brain homogenates, but weakly bound PrP from scrapie-infected brain homogenates. These results suggest that sphAb3-15 selectively recognizes PrP(C) under native conditions and that the epitope recognized by sphAb3-15 may undergo conformational changes during the conversion of PrP(C) into PrP(Sc).