The present invention relates to a method of making a β-form of a prion protein which preferably has more β-sheet than α-helix structure and is soluble in the absence of a denaturant and/or is non-aggregated and exhibits partial resistance to digestion with proteinase K. The invention also relates to use of the β-form in medicine, especially for raising to antibodies useful in the treatment and/or diagnosis of prion diseases. The invention also relates to methods of screening for compounds which are capable of inhibiting and/or reversing the conversion of the native α-form of a prion protein to a β-form, and to uses of identified compounds in medicine.