The capabilities of the U.S. Space Station Freedom (SSF) will allow a variety of scientific investigations in the biological and materials sciences. The complexity and duration of some planned investigations far surpass those flown to date on Spacelabs and carry an increased risk of accidental release of toxic compounds. This risk is further increased by the presence of large amounts of utility chemicals for SSF systems. Past experiences on Shuttle flights have confirmed the potential for airborne contamination emanating from both payload and Shuttle systems as a result of thermodegradation during flight.This paper describes the SSF Environmental Health System's air-quality monitoring strategy and instrumentation. A two-tier system has been developed, consisting of first-alert instruments that warn the crew of airborne contamination and a volatile organic analyzer that can identify volatile organic contaminants in near-real time. The strategy for air quality monitoring on SSF is designed to provide early detection so that the contamination can be confined to one module and so that crew health and safety can be protected throughout the contingency event. The use of air-quality monitors in fixed and portable modes will be presented as a means of following the progress of decontamination efforts and ensuring acceptable air quality in a module after an incident. The technology of each instrument will be reviewed briefly; the main focus of this paper, however, will be the use of air-quality monitors before, during, and after contingency incidents.