Investigations to establish whether a link exists between exposure to tannins in cotton dust and development of byssinosis require both qualitative and quantitative information about tannin types of materials in cotton dusts used for animal and human challenge experiments. Using previously reported high-performance liquid chromatographic (HPLC) procedures, analyses of extracts from several cotton dusts collected on vertical elutriator (VE) filters have been carried out. UV spectral characterization of the material eluting early from the HPLC column reveals its similarity to UV absorption spectra of a tannin preparation from cotton dust and of D-catechin, a typical tannin constituent. HPLC analysis of 2 cotton dust samples and 24 cotton and flax dust samples collected on VE filters obtained from three different laboratories reveals substantial qualitative and quantitative differences in their content of materials that elute in the tannin region.