A group of 343 workers (252 males and 91 females) employed in four poultry farms in Croatia was studied for the prevalence of acute and chronic respiratory symptoms and lung function changes. There were significantly higher prevalences of chronic cough, chronic phlegm, chronic bronchitis, and chest tightness in poultry workers than in control workers. Male poultry workers who were smokers had significantly higher prevalences of chronic cough, chronic phlegm, and chronic bronchitis than poultry workers who were nonsmokers (P<0.01). Poultry workers exposed for more than 10 years had significantly higher symptoms prevalences than those workers with shorter exposures (except among female smokers). There was also a high prevalence in poultry workers of acute symptoms which developed during the work shift. The measured FVC, FEV1, and FEF25 in poultry workers were significantly lower than predicted normal values. Workers exposed for more than 10 years had lower ventilatory capacity tests (expressed as percentage of predicted) than those workers with shorter exposures. Changes in FEV1, FEF50, and FEF25 were less pronounced than FVC. Additionally we showed that a water-soluble poultry dust extract obtained from this workplace caused a dose-related contraction of nonsensitized guinea pig tracheal smooth muscle when studied in vitro. Pharmacologic studies of this response indicate that it may result from the release of multiple endogenous mediators. Our data suggest that work in poultry farms may, for some workers, cause the development of acute and chronic respiratory symptoms and lung function changes.