Development of transmissible spongiform encephalopathies (TSEs)pathogenesis requires the presence of both the normal host prion protein(PrP-sen) and the abnormal pathological proteinase-K resistant isoform(PrP-res). PrP-res forms highly insoluble aggregates, with self-perpetuating properties, by binding and converting PrP-sen molecules into a likeness of themselves. In the present report, we show that small interfering RNA (siRNA)duplexes trigger specific Prnp gene silencing in scrapie-infected neuroblastoma cells. A non-passaged, scrapie-infected culture transfected with siRNA duplexes is depleted of PrP-sen and rapidly loses its PrP-res content. The use of different murine-adapted scrapie strains and host cells did not influence the siRNA-induced gene silencing efficiency. More than 80% of transfected cells were positive for the presence of fluorescein-labeled siRNA duplexes. No cytotoxicity associated with the use of siRNA was observed during the time course of these experiments. Despite a transient abrogation of PrP-res accumulation, our results suggest that the use of siRNA may provide a new and promising therapeutic approach against prion diseases.