Dicalcium phosphate was prepared from industrial crushed bone artificially contaminated with transmissible spongiform encephalopathy agents in two experiments carried out in an accurately scaled-down laboratory model of the industrial manufacturing process. In one experiment, 10 g of mouse brain infected with the 301V strain of mouse-passaged bovine spongiform encephalopathy agent was added to the crushed bone; in the other experiment, 10 g of hamster brain infected with the 263K strain of hamster-passaged scrapie agent was added. Samples of the infectious brain and dried dicalcium phosphate were assayed for the amount of 301V or 263K infectivity present. The titre of infectivity of the 301V-infected brain was 107·7 intracerebral ID50/g; that of the 263K-infected brain was 108·0 intracerebral ID50/g. The titres of the dried samples of dicalcium phosphate were 102·5 ID50/g in the experiment spiked with 301V and 102·7 ID50/g in the experiment spiked with 263K. The calculated clearance factors were 103·9 for the experiment with 301V and 103·8 for the experiment with 263K.