Prion diseases, a group of fatal neurodegenerative disorders, are characterized by the presence of the abnormal scrapie isoform of prion protein (PrP(Sc)) in affected brains. A conformational change is believed to convert the normal cellular prion protein into PrP(Sc). Detection of PrP(Sc) for diagnosis and prophylaxis is impaired because available Abs recognizing epitopes on PrP fail to distinguish between PrP(Sc) and normal cellular prion protein. Here, we report that an anti-DNA Ab, OCD4, as well as gene 5 protein, a well established DNA-binding protein, capture PrP from brains affected by prion diseases in both humans and animals but not from unaffected controls. OCD4 appears to immunoreact with DNA (or a DNA-associated molecule) that forms a conformation-dependent complex with PrP in prion diseases. Whereas PrP immunocaptured by OCD4 is largely protease-resistant, a fraction of it remains protease-sensitive. Moreover, OCD4 detects disease-associated PrP >10 times more efficiently than a widely used Ab to PrP. Our finding that anti-DNA Abs and gene 5 protein specifically target disease-associated DNA-PrP complexes in a wide variety of species and disease phenotypes opens new avenues in the study and diagnosis of prion diseases.