Inhalation of cotton dust has been shown to cause acute respiratory effects in guinea pigs. To identify the factor(s) responsible for these effects, an artificial dust was prepared by growing Enterobacter agglomerans on a cellulose powder. The dust contained 103 CFU/9 bacteria and 250 ug LPS/g. Guinea pigs received six hour exposures to the dust on five consecutive days. The animals were then rested for two days before additional measurements and tissues were taken. Pulmonary effects were similar qualitatively to those following exposure to cotton dust. There was a severe reaction following the first day of exposure with recovery during the subsequent weekday exposures. Pulmonary histopathology resembled that following exposure to cotton dust.