The condensed tannins present in cotton bracts extract have been shown to cause aggregation of platelets and secretion of 5-hydroxytryptamine following phosphorylation of specific platelet proteins (1). Further studies in our laboratory show that cotton bracts tannin also cause sphorphorylation of specific rabbit alveolar macrophage proteins in a dose and time dependant manner. Phosphorus-32 loaded alveol ar macrophages from New Zeal and white rabbits were subjected to dose and time challenge with tannin. Auto radiograms of cell proteins were then made following SDS-polyacryl amide gel electrophoresis. Densitometry of the radiograms was used to quantify the changes in protein phosphorylation. The results indicate that tannin is able to promote signal transduction mechanisms in alveoa macrophages. Further studies are planned to characterize what specific final events (secretion, oxidative burst, chemotaxis, etc.) these phorphorylation changes may invoke. These results may support a role for tannin as one of the initiators of the inflammatory process leading to the clinical byssinosis syndrome.