To verify a productive infection in PrPres producing PES cells, cell homogenates were bioassayed by intracerebral inoculation in a) transgenic mice overexpressing bovine PrPC (Tgbov XV), b) transgenic mice overexpressing ovine PrPC (Tgshp IX) and c) wild-type C57BL/6 mice. This evidence concerns the gene PRNP and infection.