The molecular masses of the PrPres moieties from the 2 cows were also clearly distinct from those from controls with Land H-BSE (Figure). For samples from animals with H-BSE, enzymatic deglycosylation demonstrated PrPres subtypes, 1 and 2, the latter being a C-terminal PrPres fragment of ≈12–14 kDa (6). To investigate whether the novel PrPres type corresponds to PrPres subtype 2, we compared samples from cow 2 with those from the H-BSE control by Western blot. The PrPres type from the 2 cows reported here and PrPres subtype 2 from the H-BSE control were indeed distinct (Figure). We report a novel PrPres signature in 2 cows with BSE diagnoses determined according to established criteria. Combining Western blot analysis with an epitope mapping strategy, we ascertained that these animals displayed an N terminally truncated PrPres different from currently classifi ed BSE prions (Figure). The interpretation of these fi ndings remains diffi cult because neuropathologic and systematic clinical data for the 2 cases are not available. Moreover, the tissue samples were autolyzed, and the question of whether this affected the PrPres molecular signature is of concern. Nonetheless, our fi ndings raise the possibility that these cattle were affected by a prion disease not previously encountered and distinct from the known types of BSE. To confi rm this possibility and to assess a potential effect on disease control and public health, in vivo transmission studies using transgenic mouse models and cattle are ongoing. Until results of these studies are available, molecular diagnostic techniques should be used so that such cases are not missed.