OBJECTIVES: Methacholine bronchial responsiveness and variations in the pulmonary function of workers exposed to wheat flour and a reference group were compared. METHODS: Each subject [140 men exposed to flour (bakers and pastry makers) and 77 controls] completed a standardized questionnaire. Bronchial responsiveness was quantified by measuring the slope between percentage decrements in forced expiratory volume in 1 second (FEV) and cumulative methacholine dose. FEV and peak expiratory flow (PEF) were recorded four times a day for 15 days using a handheld electronic spirometer. The variability in the FEV and PEF readings was expressed as variation coefficients (100 × standard deviation/mean). RESULTS: The mean duration of exposure to flour was 14 (SD 9) years. Rhinitis was significantly more common in the exposed group than in the control group (30.7% versus 11.7%, P=0.001). The mean FEV and PEF did not significantly differ between the two groups. The slope of the dose–response to methacholine and the variation coefficients were lower among the unexposed nonsmokers than among the exposed workers and smokers. The differences were significant for the exposed smokers. The two variation coefficients correlated with each other (r=0.82) but not with the slope of the methacholine challenge. CONCLUSIONS: Occupational exposure to flour and smoking increase bronchial responsiveness, as measured by the slope of the dose–response to methacholine and the variation coefficients of airflow. However, methacholine bronchial responsiveness and the variability of lung function do not measure exactly the same aspect of airway behavior.