Pandemic influenza is a serious threat for which public health emergency preparations are in high gear. Although the time at which a pandemic might arrive is unknown, most public health officials hold the opinion that the world is overdue for such an event. Measures to decrease person-to-person contact, improve treatment, and provide vaccine or antiviral drug prophylaxis are all important strategies to mitigate the impact of a pandemic. Even though the use of respirators and medical masks provides a secondary nonpharmacological means of preventing or slowing influenza transmission, such measures are widely considered an intervention of last resort. This report addresses the reuse of respirators and medical masks as a means of preventing or slowing influenza transmission during a pandemic should there be an insufficient supply of new respirators and masks available to those who need them. Medical masks are unfitted devices worn by an infected person, healthcare worker, or member of the public to reduce transfer of potentially infectious body fluids between individuals. Medical masks are designed to be disposable. In contrast, a respirator is a fitted device that protects the wearer against inhalation of harmful contamination, that is, it protects the wearer from others who are or might be infected. Properly fitted respirators provide better protection against airborne transmission of infection than do medical masks. Respirators can be disposable or reusable. The less expensive and more common respirators, called N95 filtering facepiece respirators are designed to be disposable. With adequate time and planning, stockpiling or ramping up production of respirators and medical masks or both would ensure a plentiful supply for all those who need them, but with limited resources and time, supplies are likely to be insufficient. Thus, reality may require that disposable N95 filtering facepiece respirators and medical masks be pushed beyond their approved uses in the hope that they will provide some level of protection beyond their intended limits of use. Moreover, individuals with no access to respirators or masks, even disposables, may feel driven to invent their own respiratory protection measures - for example, they may don woven masks not approved for medical uses in the United States or use household items such as towels or sheets. Based on the assumption that efforts to produce and stockpile sufficient supplies of disposable masks and/or respirators may fall short in the event of a pandemic, in January 2006 the Department of Health and Human Services (DHHS) asked the Institute of Medicine (IOM) to convene a committee to conduct a 90-day assessment of 1. what measures can be taken that would permit the reuse of disposable N95 respirators in healthcare settings, and, 2. what is known about the need for, and development of, reusable facemasks for healthcare providers and the general public.