The invention concerns a method for in vitro propagation of the agent responsible for transmissible spongiform encephalopathies, or prion, comprising steps which consist in: providing a culture or a glial cell line and in infecting the culture or line with the agent responsible for transmissible spongiform encephalopathies or prion. Said method enables to obtain infected cell line capable of being used to assess the efficacy of a molecule in the reduction or inhibition of the infectiosity of the prion or for detecting the prion.