The new International Union Against Tuberculosis (IUAT) bronchial symptoms questionnaire was completed by 827 subjects participating in a prospective study of respiratory symptoms and lung function in aluminum smelter workers. A modified Medical Research Council (MRC) questionnaire was also administered. Bronchial reactivity (BR) was measured in 809 subjects by metha-choline challenge using a rapid method. Factor analysis demonstrated sensible clustering of responses to items unqiue to the new questionnaire such as nocturnal, spontaneous, and postexertional dyspnea, dust-induced dyspnea and tightness, and breathing difficulty. Responses to IUAT questions concerning past asthma, wheeze, chest tightness, morning cough and sputum, and asthma medication agreed well with corresponding items from the MRC questionnaire. Questions concerning asthma, medication, dust-induced, nocturnal, and spontaneous dyspnea, chest tightness, wheeze, nocturnal cough, postex-ertional dyspnea and breathing difficulty also had high validity against the criterion of concurrently measured bronchial reactivity. It is concluded that the IUAT questionnaire is a valid asthma questionnaire.