Byssinosis is a hazardous respiratory disorder of workers in natural fiber processing industries and, in the case of cotton, is caused by exposure to respirable dust generated from leafy trash associated with raw fibers. To understand the chemical characteristics of involucral trash components that might contribute to bysinosis, we examined the human airway constricting activity and oxygen radical generating activity of dry, frost-killed cotton bracts. In response to inhalation of aerosolized bract extracts, the expiratory flow rates of human volunteers at 40% of vital capacity during partial forced expiration decreased by 3 to 32%. These values enabled us to identify two potentially byssinogenically active bract specimens, a specimen virtually inactive, and a fourth intermediately so. Using spin trapping techniques of electron spin resonance spectrometry, we found that all specimens catalyzed the generation of hydroxyl (preponderantly) and superoxide radicals from hydrogen peroxide. However, the weakest constrictor was the most potent catalyst, and vice versa. This was consistent with transition metal content of the specimens; the most potent catalyst also contained the largest amounts of those metals, suggesting a Fenton-type reaction mechanisms. Other possibilities for the inverse relationship of airway constricting (byssinogenic) activity with oxygen radical generation are discussed. We also found that neither aflatoxin nor endotoxin, contingent contaminants of bracts, catalyzed oxygen radical production from hydrogen peroxide.