Based on results of previous animal studies in which cotton bracts tannin promoted the recruitment of neutrophils into the airways, the ability of tannin either to function as a direct neutrophil chemotaxin or to release neutrophil chemotactic factor (NCF) from alveolar macrophages was examined. Over the concentration range of 6 to 2000 ug/mL, tannin had no direct chemotactic activity towards neutrophils. However, when incubated with alveolar macrophages, it promoted the time and dose dependent release of NCF. Maximal release occurred two to four hours after the onset of exposure at a tannin concentration of 23 ug/mL.Studies using (5l)Cr labeled macrophages indicated that this NCF release occurred without cytotoxic damage to the macrophages. These results suggest that tannin mediated release of NCF from alveolar macrophages is one possible mechanism for the recruitment of neutrophils into the airways which occurs in byssinosis.