Title 42, Code of Federal Regulations, Part 84 (42 CFR 84), states the minimum face piece fit requirements: “Half-mask face pieces and full face pieces shall be designed and constructed to fit persons with various facial shapes and sizes….” Compliance with this requirement is verified by performing an isoamyl acetate (IAA) fit test. In the late 1970s, an evaluation conducted by Los Alamos National Laboratory determined that for air-purifying respirators, this test should be performed using a panel of test subjects of various facial sizes as determined by this study. There are two panels, one for half-mask face pieces and one for full face piece respirators, both conventionally referred to as the LANL panel. Performing this test with the LANL panel of test subjects is done to ensure that a respirator, fitted according to the manufacturer’s User’s Instructions and passing the manufacturer’s prescribed user seal check, will protect as expected and maintain a proper fit. Although NIOSH is developing a new panel based on recent research, the LANL panels are currently still in use. Persons interested in the details of the measurements for selecting the face sizes for the LANL panel groups may contact the National Institute for Occupational Safety and Health, National Personal Protective Technology Laboratories, by phone at 412-386-4000, or by e-mail at npptl@cdc.gov. Additional details about the new panel can be found at www.cdc.gov/niosh/npptl/resources/pressrel/letters/lttr-051805.html.