The frequency of bronchial symptoms and the alteration of respiratory function parameters were studied in a group of 63 workers of an industrial flour-mill, and in a control group matched according to age, social class, and tobacco intake. In the exposed group the answers to a questionnaire indicated a greater incidence of cough (p less than 0.01) and chronic expectoration (p less than 0.01) as well as clinical airway hyperreactivity (p less than 0.01). No differences were noted for either asthma or allergy. The respiratory function parameters did not differ between the two groups studied. These results suggest that workers exposed to the vegetable dust found in fluor-mills are subject to develop chronic bronchial irritation.