We describe the quality of a rabbit polyclonal antiserum (Sal1) that was raised against mature human recombinant prion protein (rhuPrP). Epitope mapping demonstrated that the Sal1 antiserum recognized six to eight linear antigenic sites, depending on the animal species. The versatility of the antiserum was evident from the range of animal species and immunochemical techniques where it could be applied successfully. Antigen absorption studies revealed differences in the location and number of epitopes remaining after incubation with soluble or aggregated antigen.Our knowledge concerning immunoprophylaxis against prion diseases and the important role played by conformational changes of PrP is increasing rapidly. The findings reported here should add to this body of knowledge.