We have produced a mouse model of a familial prion disorder by introduction of a transgene that encodes the moPrP homolog of a nine-octapeptide insertional mutant associated with an inherited form of CJD in humans. These mice develop progressive neurologic symptoms, display neuropathologic changes, and accumulate a form of mutant PrP in their brains and peripheral tissues that displays some of the biochemical properties of PrPSc. These mice have been extremely valuable for analyzing the cellular and biochemical mechanisms involved in inherited prion disorders and correlating the appearance of the PrPSc-like form with clinical and neuropathologic findings. Because the mutant protein in the mice is highly neurotoxic but appears to lack infectivity, further analysis of its properties promises to shed new light on the molecular distinction between pathogenic and infectious forms of PrP.