A possible impact of physical load on the degree of bronchial hyperreactivity was studied in actual working conditions among the workers in an aluminium electrolysis plant. Respiratory irritants present in the working environment were also determined. The study was conducted in two groups of workers: one, of 34 workers who had been previously categorized as having respiratory symptoms and the other, of 19 control workers without symptoms. Both groups were matched by age, height, weight and years of service in the plant. All workers underwent a progressive submaximum exercise test of 300-600-900 kpm/min load on a bicycle ergometer. Simultaneously a continuous monitoring of heart function was performed. Heart rate, blood pressure and lung function parameters: FVC, FEV1, PEF, MEF25, MEF50, MEF75 and FEV1/FVC% ratio were measured before and 18 minutes after exercise. The results of the study showed that physical load and concurrent exposure to respiratory irritants had no impact on bronchial hyperreactivity in either group of workers. However, the exercise test demonstrated the existence of appreciable individual differences within the two groups.