Endotoxin was obtained from Enterobacter agglomerans, a gram-negative bacterium commonly associated with cotton dust, by the method of Boivin et al. (1). Guinea pigs were exposed for 3 hours to aerosols nebulized from solutions containing various concentrations of endotoxin (0.1 µg/ml to 3.3 mg/ml). Pulmonary responses 18 hours after exposure were as follows: 1) breathing rate, total lavagable cells, lymphocytes and red blood cells increased in a dose dependent manner, peaking at 1.0 mg/ml; 2) granulocytes increased by 74-fold at 1.0 )µg/ml before declining to a 34-fold increase at 3.3 mg/ml; 3) alveolar macrophages initially declined by 27% at 0.1 µg/ml endotoxin before increasing by 57% at 1.0 mg/ml; and 4) zymosan-stimulated superoxide release increased 102% at 3.3 mg/ml endotoxin. In conclusion, inhalation of E. agglomerans endotoxin resulted in pulmonary responses which were qualitatively similar to those seen with cotton dust.