In this study three different cotton dust extracts were inhaled by human volunteers to establish which extracts have bronchoconstrictor activity. The three preparations were the crude aqueous extract, acetone precipitate fraction (polymer) and the acetone soluble fraction (the rest). An equivalent of 6g of whole dust in 50ml saline was aerosolized and inhaled for six minutes for each fraction. Specific airway conductance was measured by constant volume whole body plethysmography. All three extracts produced an initial bronchoconstriction (one minute after the end of inhalation) in all four subjects, and a secondary response (later onset and longer duration) was produced for all three extracts in three out of four subjects. The fourth subject had a secondary response with the aqueous extract but not the polymer or 'the rest'. Bronchoconstrictor activity of cotton dust extracts can therefore be resolved into acetone precipitate and acetone soluble components as well as the aqueous extract.