BACKGROUND Power plant workers are potentially exposed to nitrogen dioxide (NO2) and may therefore be at higher risk of pulmonary diseases than the general population. AIMS To assess the association of NO2 exposure with spirometric abnormalities in power plant workers. METHODS Forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC) and forced expiratory ratio (FER = FEV1/FVC) were correlated with demographic characteristics, smoking history and environmental exposure to NO2 in power plant workers exposed to environmental NO2 at work and in a control group of administrative employees. Twenty-four hour environmental NO2 concentrations were measured at each workplace. RESULTS The concentrations of environmental NO2 ranged from 1.21 to 7.82 mg m(-3) with a mean value of 3.91 + 1.51 mg m(-3). The results showed that FEV1 and FVC were significantly lower in 347 power plant workers than in the 349 controls (P < 0.001). The FER was significantly correlated with age, environmental NO2 concentration, smoking and height. CONCLUSIONS Occupational exposure to NO2 emissions in power plants is significantly associated with lung function abnormalities as assessed by spirometry. Spirometric measurements in power plant workers exposed to NO2 emissions may be an effective means of detecting early signs of impaired respiratory health in this group of workers.