Pulmonary effects, lung clearance, and tissue retention of blood-bornePseudomonas aeruginosawere compared in dogs (n= 5) and pigs (n= 5) during continuous 6-hour intravenous infusion of 1.2(109) bacteria/min/20 kg. Control pigs received an equal volume of sterile saline. In contrast to controls, experimental pigs developed pulmonary artery (PA) hypertension (mean, 30 ± SE 3; baseline, 17 mm Hg) and pulmonary failure manifested by hypoxemia (mean Pao2, 49 ± 4; baseline, 78 ± 2 mm Hg;p< 0.001), increased intrapulmonary shunting (40 to 50%), noncardiogenic pulmonary edema, and congestive atelectasis, a pattern of pulmonary failure very similar to sepsis-induced ARDS in humans. In dogs, PA pressures were unchanged from baseline, no edema was detected, and comparable hyperventilation was associated with an increase in Pao2from 77 ± 4 (baseline) to 87 ± 2 mm Hg (p< 0.001). Tissue retention of viable blood-borne organisms in pigs was greatest in the lungs. In dogs, lung retention was minimal and greatest tissue retention occurred in the liver and spleen. We conclude that both lung clearance of blood-borne organisms and bacteremia-induced pulmonary failure are quite host dependent.