In prion diseases, the normal cellular form of prion protein (PrP^C) is converted into the disease-associated isoforms (PrP^Sc) which accumulate in the infected tissues. Although the precise mechanism of this conversion remains unsolved, drugs of various categories have been reported to reduce the accumulation of PrP^Sc in prion-infected cultured cells. We here show that AY-9944 (a 7-dehydrocholesterol reductase inhibitor) and U18666A (a 24-dehydrocholesterol reductase inhibitor) prevent PrP^Sc from accumulating in prion-infected mouse neuroblastoma cells (ScN2a), with an ED₅₀ of about 0.5 μM and 10 nM, respectively. In order to evaluate the efficacy of these two inhibitors in vivo, C57BL/6J mice inoculated with mouse-adapted scrapie-prion received repetitive intraperitoneal injections of U18666A (10 mg/kg) or a mixture of U18666A (10 mg/kg) and AY-9944 (12 mg/kg). By contrast to the potent anti-prion effects observed in ScN2a cells, the in vivo trial was abortive with neither drug halting the progression of the disease.