Inhalation of cotton dust released when raw cotton is processed in textile mills can lead to byssinosis, a pulmonary disease of textile mill workers. Endotoxins, components of gram-negative bacterial cell walls, which also are found in cotton dust, are believed to cause many, if not most, of the symptoms of byssinosis. Cotton dust treated with sodium hydroxide in alcohol showed reduced endotoxin levels and reduced toxicity in guinea pig pulmonary assays. The original detoxification experiments were conducted on a dust (DB 11/82) from the Memphis area. Results for a new cotton dust (DB 1/88) have been compared with those for DB 11/82. Endotoxin levels, as measured by the Limulus amebocyte lysate assay, were reduced by 95% or more by sodium hydroxide treatment or by repeated water extractions. Dimethyl sulfoxide was not effective in reducing the endotoxin content of cotton dust, although it has been reported to quantitatively extract endotoxin from natural substrates. Thus, alcoholic sodium hydroxide is currently the most reliable treatment for reducing the endotoxin content and pulmonary toxicity of cotton dust.