Although bacterial endotoxins are a prime suspect in the acute and/or chronic response to cotton dust, other chemical constituents of cotton dust may contribute to the responses. These other constituents can be affected by treatments developed to deactivate endotoxins in cotton dust or fiber. For instance, condensed tannins in the cotton plant are degraded by alkaline treatment. A previously developed alkaline treatment (which has been shown to deactivate endotoxins in cotton dust and reduce pulmonary toxicity of the dust in a guinea pig animal model) was applied to cellulose powder coated with condensed tannins extracted from cotton dust DB 1/88. In this paper we report on the physiological activity of dust DB 1/88, extracted dust, tannin-coated powder, and alkali-treated tannin-coated powder, by comparing their ability to stimulate production of arachidonic acid metabolites in guinea pig pulmonary cells obtained by lung lavage. Physiological activity will be related to tannin and endotoxin content of the dusts and powders.