Two experimental cottons were grown, harvested, and processed identically except that one had all bracts removed prior to boll opening in the field. Removal of bracts resulted in ginned cotton lint with a significantly lower leaf trash index, but cardroom dust levels were not decreased. A group of healthy subjects, selected for acute airway reactivity to cotton dust, had spirometry before and after 6-hour exposures to card-generated cotton dust from each of the two cottons. For exposures to dust from the bracted and bractless cottons, mean vertically elutriated dust concentrations were equal (0.51 mg/m³). Likewise, for the group of 27 subjects with valid complete data, the overall mean FEV(1) responses were equivalent (-4.0% and -4.2% for dust from bracted and bractless cotton respectively). Both responses were different (p < 0.05) from the mean FEV(1) response of +0.7% to control (no dust) exposures.