Dilution series of keratinase digested non-heated BSE material to quantify the PrPSc removal by keratinase in the heated sample. Lanes 1 and 2 represent heated and digested BSE-negative (N) and positive (B) material, while lanes 3–8 show a non-heated and digested BSE-sample in a four-fold dilution series in reverse order. Amount of tisssue equivalents (TE) applied per lane are indicated in µg. The signal of PrPSc in lane 2 was similarly negative to that of the BSE-negative sample in lane 1, and lower than the lowest amount applied of heated and non-digested BSE sample in lane 3 i.c. less than that in the 0.5 µg TE lane. This means that removal of PrPSc from 500 µg TE in lane 2 was more than 99.9% based on the applied TE which corresponds to a > 1000 × reduction factor. The parallel blots were stained with antibodies 94B4 and Sha31 (0.1 µg mL−1). TE in µg, gels were run in parallel in MOPS buffer.