The epidemic of bovine spongiform encephalopathy (BSE) in the UK has led to concerns that transmission to man may occur through dietary exposure. The recognition of a new variant of Creutzfeldt-Jakob disease (nvCJD) in unusually young people in the UK suggested that this may already have occurred. Supportive evidence for such a link with BSE is provided by experimental transmission studies of BSE in the macaque and by the identification of a biochemical marker that differentiated nvCJD from previously recognised sporadic and iatrogenic CJD, but which resembled BSE and BSE passaged in other mammalian species. Western blot analysis of proteaseresistant prion protein (PrP) in sporadic and iatrogenic CJD reveals three distinct patterns (types 1–3) distinguished by fragment size after proteolysis with proteinase K, while nvCJD differs from all these types by a distinctive pattern of prion-protein glycoform ratios, designated a type 4 pattern. This molecular analysis has already been used in the differential diagnosis of a suspected case of nvCJD case.