Positron emission tomography (PET) uses a subset of radioactive pharmaceuticals to determine biochemistry, physiology, anatomy, and pathology within various body organs and tissues by measuring the concentration of radioactivity in a targeted area of the body. The active component of PET drugs is a positron-emitting isotope. PET drugs are not manufactured by pharmaceutical companies; instead, they are prepared by physicians and pharmacists operating accelerators in facilities known as nuclear pharmacies, which most often are part of major teaching hospitals or their adjacent universities, and always are located very near to the place where the PET drug will be administered to patients. On February 25, 1995, FDA (D) announced that PET radiopharmaceuticals 'should be regulated' under the drug provisions of the Federal Food, Drug, and Cosmetic Act. The Administrative Procedure Act’s (APA’s) notice and comment procedures do not apply to an agency’s non-substantive statements. D characterized the 1995 notice as a non-substantive guidance or policy statement and did not provide notice and comment. d indicated that its 1995 publication was to supersede its prior 1984 publication. The 1984 Guideline had unequivocally stated that nuclear pharmacists who operated an accelerator to produce radioactive drugs to be dispensed under a prescription-which precisely describes the process by which nuclear pharmacies compound PET radiopharmaceuticals--were not required to register under § 510 of the Federal Food, Drugs, and Cosmetics Act (FFDCA). The 1995 notice reversed that position. P filed suit alleging in part that D violated the APA requirement that an agency engaged in rulemaking give notice of its proposed rulemaking to the public. The district judge granted summary judgment in D's favor. P appealed.