There is a limited number of reports regarding detergents and proteases inactivating, degrading, or destabilizing abnormal prion protein (PrPSc). In the present study, the effect of alkaline detergents and proteases on the breakdown of PrPSc in the absence of proteinase K (PK) (degradation) and the presence of PK (destabilization) was investigated. PrPSc from brain homogenate of terminally-diseased mice infected with the Chandler strain of scrapie was used as a substrate. A surfactant-free alkaline detergent (pH 11.9, 1% aqueous solution) with potassium hydroxide as the main ingredient and an alkaline detergent (pH 11.9, 1% aqueous solution) containing about 1% surfactant as well as two commercially available alkaline proteases had a destabilizing effect on PrPSc. All these detergents and proteases showed degradative effects on PrPSc under appropriate conditions. These results demonstrate the usefulness of alkaline detergents and proteases for the degradation or destabilization of PrPSc.