Evolution of bronchial reactivity was examined in a sample of aluminium potroom workers exposed to a variety of respiratory irritants in concentrations below the MAC values for Yugoslavia (hydrogen fluoride, particulate fluorides, sulphur dioxide). Lung function indices and bronchial reactivity were measured in 24 workers continuously employed in an aluminium plant and in nine workers who had ceased to work in the plant. Measurements took place over a two-year interval. A sustained level of bronchial reactivity was recorded in both examined groups regardless of occupational practice. Even in workers with dyspnoea and airway obstruction bronchial reactivity did not worsen in spite of continuous exposure. Avoidance of exposure to potroom fumes did not bring about any significant improvement of reactivity, moreover, bronchial reactivity deteriorated in one worker. Owing to discordance between spirometric values and bronchial reactivity, a follow-up of workers removed from harmful occupational exposure is suggested.