OBJECTIVES: The aim of this study was to determine associations between lung function, bronchial hyperresponsiveness (BHR), and atopy with exposure to fire smoke among firefighters. METHODS: The study was comprised of 402 firefighters, a randomly chosen subset of a previous survey among firefighters in the Netherlands. Subjects underwent spirometry and methacholine provocation, and blood samples were taken to assess atopy. Exposure to fire smoke was registered by a questionnaire. RESULTS: Hyperresponsiveness expressed as dose-response slope (DRS) was positively and significantly associated with the number of fires fought in the last 12 months with and without adjustments for smoking, gender, atopy, age, and exposure in the main job held. Limiting the analysis to firefighters without exposure within 7 days of testing did not change any of the associations. The association between the number of fires and the DRS was stronger among atopics, and hyperresponsiveness expressed as PD (20)was also significantly associated, indicating that atopics are at higher risk of developing BHR as a result of smoke exposure. Respiratory protection devices were not optimally used. CONCLUSIONS: It is recommended that awareness be heightened among firefighters to avoid exposure to all fire smoke and that management be sensitive to the adequate use of self-contained breathing apparatuses by their personnel