We studied the pharmacologic properties of a water soluble extract of cotton bract (CBE) using isolated guinea pig trachea. Dose response relationships between CBE and contractions of guinea pig tracheal smooth muscle were established. The effects of pre-treatment with indomethacin, LY171883, spiperone, atropine and pyrilamine were measured on the tracheal response to CBE. Partial protection against CBE induced contraction was demonstrated for pyrilamine, LY171883, atropine and spiperone suggesting that, in this system, CBE may act by the release of several tissue active mediators.