We speculate that Tg(M109) mice inoculated with BVPrP-adapted sCJD or vCJD prions may constitute an excellent system for performing initial assessments of the in vivo efficacy of candidate CJD therapeutics, although weak therapeutic effects may be harder to discern in mice with such rapid incubation periods and positive results would need to be confirmed in Tg mice expressing human PrP. This evidence concerns the gene PRNP and Creutzfeldt Jacob disease.