Sporadic and variant Creutzfeldt-Jakob disease brain reference materials available from the UK National Institute for Biological Standards and Control have been subjected to further characterisation by Western blot analysis, with particular reference to the co-occurrence of different abnormal disease-associated prion protein (PrP(Sc)) types. The results confirm the presence of genuine type 1 and type 2 protease-resistant PrP (PrP(res)) in each of the three sporadic Creutzfeldt-Jakob disease reagents, and provide evidence supporting the lower level presence of type 1 PrP(res) in the variant Creutzfeldt-Jakob disease reagents. We conclude that these reagents provide a valuable resource for future research and development.