The effect of cotton dust on synthetic dipalmitoyl lecithin (DPL) at the air- liquid interface was studied using a Wilhelmy type balance. The results indicate that some surface active materials are part of or are absorbed on the cotton dust particles. When the cotton particles were washed with water, methanol, and/or chloroform and then sprinkled onto the subphase, the hysteresis decreased slightly. In addition, when the washed particles (5 mg) were sprinkled onto the DPL film, the hysteresis decreased to 30% (N=3) and the minimum surface tension slightly increased. These results show that the solvents only extracted part of the surface active material from the cotton dust.