In January 2004, the National Institute for Occupational Safety and Health (NIOSH) received several requests from the Transportation Security Administration (TSA) to conduct health hazard evaluations (HHEs) at four international airports: Palm Beach, Florida (PBI): Miami, Florida (MIA); Washington-Dulles, Dulles, Virginia (IAD); and Baltimore-Washington (BWI), Linthicum, Maryland. The requests expressed concern that contaminants found in the emissions of tug engines operating near "checked baggage" screening areas were related to health problems reported by some TSA employees, including respiratory distress, dizziness, and headaches. After conducting initial site visits in early 2004, NIOSH investigators returned to each airport and between April 2004 and July 2004, conducted general area and personal breathing zone (PBZ) air sampling for diesel exhaust (measured as elemental carbon [ECD, nitrogen dioxide (NO2), nitric oxide (NO), carbon monoxide (CO), and volatile organic compounds (VOCs). Overall, an inhalational hazard from tug exhaust emissions did not exist at the time of the surveys. However, air contaminant concentrations may vary due to a number of factors, such as dilution ventilation, natural ventilation, and the use of pedestal-type fans. Also, contaminant concentrations could increase if tugs are not properly maintained, sit in idle mode for extended periods of time, ventilation systems are rendered inoperable or ineffective due to damage and/or lack of maintenance, or if tug traffic increases. Weather conditions such as stagnant outdoor air may also cause contaminant concentrations to increase. Thus, even though the contaminant concentrations were below relevant occupational exposure limits at the time of these surveys, it is important to ensure that tug emissions are kept as low as possible by performing routine mechanical services, including engine tune-ups, air filter changes, and oil/oil filter changes. Ideally, electric powered tugs should be used when replacing unusable gasoline, propane, or diesel powered tugs. The "on-demand" ventilation system that operates based on CO concentrations could potentially control CO and other tug emissions if that type of system is installed and maintained in other airports where the baggage screening areas are mostly enclosed. The large pedestal-type fans in each screening area appeared to provide some cooling relief to the workers when the ambient temperature and humidity increased. However, the effectiveness of the pedestal-type fans in controlling airborne contaminants was not evaluated in this study.