Endotoxin levels were quantified in airborne cotton dust which was generated during carding operations at two model cardrooms. Pulmonary function measurements were conducted on healthy volunteers, and correlations between acute pulmonary function decrements and endotoxin levels were made. Washing experiments showed that water washing, bleaching, or bleaching and scouring were all equally effective in reducing the airborne endotoxin levels and pulmonary function changes to the dusts. Unwashed cottons from geographically different growing areas produced dusts which differed markedly in endotoxin content, and the pulmonary function changes follow the endotoxin concentrations fairly well. The data suggest that quantification of airborne endotoxin exposure may be a good biological indicator of the "cleanliness" or "potency" of the cotton.