The most important question-yet still unsolved-raised by the mad cow d
isease (Bovine spongiform encephalopathy) crisis in Europe is that of
its eventual transmission to man. The recent description of variant ca
ses of Creutzfeldt-Jakob disease in man, with peculiar features increa
ses the concern. This paper intends to describe the different paramete
rs involved in interspecies transmision of spongiform encephalopathies
.