The effect on airway responsiveness of an oral dose of a beta-adrenergic blocker (80 mg propranolol) given before work, was studied in 15 potroom workers who complained of dyspnoea, chest tightness and wheezing after they had started to work in potrooms. The same study was performed in a group of 10 potroom workers, selected at random, who had not complained of such symptoms. In addition, another group of 12 potroom workers with respiratory symptoms were given 1 mg atropine subcutaneously. Ventilatory function was assessed from forced expiratory curves (by means of a waterless spirometer) and from maximum expiratory flow-volume curves (by means of a digital pneumotachograph). Bronchoconstriction during the first few hours' work was significantly potentiated by propranolol in the group of potroom workers with respiratory complaints. Propranolol did not produce this effect in workers who had not complained of respiratory symptoms. Atropine sulphate abolished the fall in ventilatory volumes which occurred during the first few hours of work. These findings suggest that acute bronchoconstriction, particularly in small airways, and respiratory symptoms occurring in certain potroom workers may be based on an alteration in autonomic balance with vagal preponderance.