On the basis of reduction in endotoxin content, a number of studies have suggested that cotton dust may be "detoxified" through heat treatment (typically, 252°C,20 sec.). Attempts to separate those components of cotton dust aqueous extract (CDE) responsible for the contraction of the rat stomach fundus (RF) by thin layer chromatography (TLC), prompted an investigation into the susceptibility of these components to autoxidation. In freeze-dried form, 80% of the RF activity was lost at 100°C (1hr.) and 100% at 120°C. However, boiling solutions of CDE did not result in significant loss of potency, suggesting that the RF contractor agent(s) are more heat-stable in solution. Whist stable in freeze-dried form, in the presence of air or oxygen in solution, at least the major RF contractor agent is prone to autoxidation at room temperature. Aeration of the aqueous solution resulted in loss of potency. Following application to TLC plates, the RF activity of CDE was lost even though the maximum temperature used in the procedure was 60°C (in the "rotavap" drying stage). Silica and alumina gels are known to promote autoxidation, providing further evidence of the susceptibility of these components. Some parallels have been demonstrated between fractions of CDE active on some smooth muscle tissues and acute in vivo responses in guinea pigs. Further investigation may reveal the possibility of a measure of "detoxification" through mild treatments without significant damage to fibre quality.