On February 21, 1997, the National Institute for Occupational Safety and Health (NIOSH) received a request from Northwest Airlines (NWA) customer service agents (CSAs) to investigate ongoing health complaints among NWA employees at Wayne County Airport in Detroit, Michigan. Employees expressed concern that certain symptoms such as difficulty breathing, headache, fatigue, nausea, and miscarriages may be related to the indoor environmental quality (IEQ) at the airport. The requesters identified several agents of concern including malodorous sewer gas, carbon monoxide (CO), carbon dioxide (CO2), and glycols. In response to the request, NIOSH investigators reviewed the results of previous IEQ investigations conducted at the airport and visited the airport on February 9-10, 1998. NIOSH investigators focused on those agents which were of the greatest concern to employees and to which exposure seemed plausible. These included measurements of CO and odors. NIOSH also sought to better understand the types and patterns of symptoms experienced by CSAs.