In a cross sectional study of a working population of black South African gold miners a sample of 1197 older miners was examined. Airway reactivity determined by a greater than 10% response of the forced expiratory volume in one second (FEV1) to inhaled salbutamol was detected in 139 (12%) of the men. No relation was found between the extent of exposure to the underground environment and the frequency of airway reactivity. There was evidence of increased chronic airflow limitation in the men with reactive airways. This increase persisted after controlling for age, tobacco smoking, and for the presence and degree of silicosis. On average, the presence of reactive airways was associated with reduced (after bronchodilator) forced vital capacity (FVC) of 118 ml, 95% confidence interval (CI) 16 to 220 ml, FEV1 of 168 ml (95% CI 74-262 ml), FEV1/FVC% of 3% (95% CI 2.3-3.7%), and maximal mid-expiratory flow of 300 ml/s (95% CI 86-514 ml/s). Although there was no evidence that airway reactivity was induced by this occupational exposure, those with reactive airways appeared to be more susceptible to the adverse effects of the underground environment on the bronchial tree.