To assess the prevalence and the characteristics of exercise-induced bronchoconstriction (EIB) in subjects occupationally exposed to organic dusts we performed a cross-sectional study including 152 exposed subjects (67 textile workers, 42 agricultural workers, and 43 bakers) and 72 unexposed controls. Evaluation of exposed and unexposed subjects included a questionnaire, skin prick tests to common inhalant allergens, spirometry, and exercise challenge tests (ECT). The EIB prevalence found in textile workers was 8.9 %, in agricultural workers 7.1 %, in bakers 6.9 %, and in office workers 5.5 %. The highest bronchial reaction to exercise was found in ECT-positive agricultural workers (26.1+/-6.9), followed by textile workers (25.2+/-7.4), bakers (23.0+/-5.8), and office workers (21.8+/-4.4). EIB was significantly associated with atopy and positive family history of asthma in all exposed groups. EIB was significantly associated with smoking duration in textile workers (P=0.039) and agricultural workers (P=0.027). Bronchial reaction to exercise was significantly greater in smoking than in non-smoking textile (P=0.045) and agricultural workers (P=0.032). Our data suggest that the combination of daily smoking and workplace exposure to certain types of organic dusts could contribute to EIB development and severity.