With this final rule EPA declares a prion (i.e., proteinaceous infectious particle) to be a "pest" under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and amends the regulations to expressly include prion within the regulatory definition of pest. This final rule also amends existing pesticide product performance data requirements to clarify that efficacy data are required for pesticide products with prion-related claims. In addition, EPA is announcing the availability of final test guidelines on generating the product performance data for prion-related pesticide products.