Biochemical typing of scrapie strainsDifferences in the molecular heterogeneity of the abnormal isoforms of the prion protein, PrP 5 c, due to differential glycosylation and partial endogenous or exogenous proteo-lysis1'2 have been found in different scrapie strains\ sources of Creutzfeldt-Jakob disease (CJD) and fatal familial insomnia (FFI) 4 ';, Recently Collinge et a/. 6 extended this analysis to include sporadic CJD and the new variant of Creutzfeldt-Jakob disease ( vCJD) and found that the vCJD 'type 4' pattern of PrPSc was common to mice, cats and monkeys infected with bovine spongiform encephalopathy (BSE). We have extended this analysis to include scrapie strains passaged in mice and originally derived from sheep or goats.Collinge et a/. 6 suggested that the prion molecular phenotype 'type 4' was distinct and characteristic ofBSE, and that its presence in vCJD was further evidence of a direct link between vCJD and BSE. Furthermore, they suggested that this pattern, though also seen in FPC, might be used to identify a BSE origin of the disease-in particular that it would differentiate BSE and natural scrapie in sheep and goats. Unfortunately, no control data of scrapie in mice or the other species were given to support this idea.We present a glycoform ratio analysis of mouse-passaged scrapie strains from sheep or goats and compare them with a BSE-60 ~ I 20 40 60 80 100 PrPSetn high Mr glyco!Ofm (%)