The airway response (sGaw) of four healthy volunteers to inhaled aerosols of cotton dust extract has been studied using whole body plethysmography. A doseresponse relationship was examined in three of the subjects but was not found to be very striking over the concentration range employed. The pharmacological agents terfenadine, cromoglycate, nedocromil, oxatomide, vitamin C, ibuprofen and ketoconazole were unable to significantly modify the response of the subjects to inhaled dust extract. However, verapamil antagonised the effects of low but not high doses of inhaled extract. The results confirm that the acute bronchoconstrictor effects of inhaled cotton dust extracts are unlikely to be mediated by release of histamine, mast cell products and prostanoids. The response appears to be markedly calcium dependent.