Airway hyperreactivity has been reported in cotton mill workers. By contrast, hyporeactivity has been reported in guinea pigs exposed acutely to a very high concentration of cotton dust (1). We tested the hypothesis that changes in airway reactivity were related to the concentration of cotton dust inhaled. Groups of guinea pigs were exposed to increasing concentrations of cotton dust (0.15 - 9.1 mg/m³), for 6 hours. Airway reactivity was assessed at various time intervals. Minor changes in airway reactivity were noted immediately following inhalation of the dust. However, the hyperreactivity reported in workers was not found in this animal model.