Morphometric analysis of lung tissue from hamsters exposed to aerosols of LPS from E. agglomerans was conducted in an effort to ascertain changes induced by one of the suspected etiologic agents of acute byssinosis. Hamsters were exposed to up to 5 daily 5 hr doses (4 ug/m³) in an effort to simulate changes occurring throughout the workweek. Analysis was carried out on animals receiving saline aerosol (controls, n=6) and on animals sacrificed either 6 hrs after the first daily exposure (n=6), 24 hrs after the first daily exposure (n=6) or 6 hrs after the fifth daily exposure (n=5). The distal lung air space and volume densities (V(v)) of polymorphonuclear leukocytes (PMNS) and of platelets in the pulmonary capillary blood were significantly different from control values 6 hrs following a single exposure. By 24 hrs, these changes were declining back toward control values. Six hrs following the fifth daily exposure, no significant differences were seen with regard to these parameters, but an examination of cells migrating into the distal lung airspace revealed a significant increase in V(v) of PMNs in alveoli. In addition, the mean air-blood barrier thickness of the latter group was significantly increased versus all other groups. These results indicate that repeated aerosol exposure to LPS can alter or eliminate changes seen after a single LPS exposure. Elucidation of these changes may help in the determination of responses which are important to the pathogenesis of acute byssinosis.