In 1988, the Environmental Protection Agency (EPA) discovered four pesticides to be carcinogens. The Delaney clause of the Federal Food, Drug, and Cosmetic Act (FFDCA), 21 U.S.C. § 348(c)(3), prohibited the use of pesticides found to induce cancer as food additives. However, EPA regulations permitted the use of these four pesticides as food additives. Kathleen Les and several other individuals (plaintiffs) asked the EPA to revoke these regulations. However, the EPA refused to do so, reasoning that the cancer risk from the four pesticides was de minimis. The EPA issued a final order declining to revoke the regulations. The plaintiffs petitioned for review in the United States Court of Appeals for the Ninth Circuit. The EPA relied on a scientific study to argue for a de minimis exception to the Delaney clause that would permit a more reasonable and realistic approach to minimizing the public’s exposure to cancer-causing additives.