This regulation establishes tolerances for the combined residues of mefenpyr-diethyl also known chemically as 1-(2,4- dichlorophenyl)-4,5-dihydro-5-methyl-1H-pyrazole-3,5-dicarboxylic acid, diethyl ester in or on wheat and barley commodities. Bayer CropScience formerly doing business as Aventis CropScience and/or AgrEvo Company requested this tolerance under the Federal Food, Drug, and Cosmetic Act (FFDCA), as amended by the Food Quality Protection Act of 1996 (FQPA).