The Health Hazard Evaluation Program carried out a study at a fire service training facility to assess exposures to airborne polycyclic aromatic hydrocarbons (PAHs) and other aromatic hydrocarbons. The purpose was to learn whether these substances pass through the skin of firefighters wearing full ensembles. Some PAHs and other aromatic hydrocarbons are known or suspected of causing cancer. The study consisted of two rounds (1 year apart). In each round, five firefighters fought a controlled structure burn once a day for 3 days. Firefighters wore new or freshly laundered turnout gear each day and wore self-contained breathing apparatus (SCBA). The burns took place in a timber-framed structure or a metal container; interior walls were covered with drywall. The rooms were set up with typical family room furniture. The burns lasted an average of 22 minutes. Firefighters' activities included an average of 11 minutes watching the fire build, 3.5 minutes knocking down the fire, and 7.5 minutes doing overhaul. We collected air, breath, urine, and wipe samples of the skin (forearms, hands, neck, face, and scrotum) throughout the day. We analyzed the samples for PAHs and aromatic hydrocarbons in the air, PAHs on firefighters' skin before and after firefighting, and PAHs and aromatic hydrocarbons in firefighters' blood and urine before and after firefighting. The air samples showed that all the burns released PAHs into the air. The PAH levels were the same or higher than levels reported in other firefighting studies. The levels of PAHs in air during five burns were higher than the occupational exposure limit. The air levels decreased after knockdown but remained above the occupational exposure limit during overhaul. Firefighters do not always wear SCBA during overhaul. The biological monitoring showed that (1) the PAH levels on fire fighters' necks (least protected body area) were higher right after the burns than before (PAHs were not found on other areas of fire fighters' skin), (2) levels of PAHs excreted in urine 3 hours after firefighting were higher than those excreted just before or just after firefighting, and (3) benzene was the main aromatic hydrocarbon measured in fire fighters' breath at levels that were higher just after firefighting than just before (we detected no benzene in urine after firefighting). HHE investigators determined that the levels of PAHs and benzene in firefighters' bodies were similar to levels in occupational groups with low exposures to these compounds. PAHs and benzene likely entered their bodies through their skin because most fire fighters wore properly working SCBA. The following recommendations were provided: (1) maintain and routinely test SCBA to ensure proper function, (2) require firefighters to wear full protective ensembles, including SCBA, during knockdown and overhaul for all fire responses, (3) provide firefighters with long hoods that are unlikely to come untucked, (4) provide as much natural ventilation as possible to burned structures before starting investigations, (5) take off gear before entering a rehab area; remove SCBA and hood last, (6) store gear on the outside of the apparatus when riding back to the station, and (7) wash hands immediately and shower as soon as possible after a fire response. A five page summary report is also available.