Hemodynamic and pulmonary gas exchange consequences of 20 percent intravenous fat emulsion infusion (3.0 +/- .3 mg/kg/min) were evaluated in 19 patients who demonstrated ARDS. Lipid infusion precipitated a significant reduction in PaO2/FIO2 from 241 +/- 50 to 184 +/- 41 (mean +/- SD) and increased MPAP from 26.0 +/- 5.1 to 31.8 +/- 4.8 mm Hg, pulmonary vascular resistance from 149 +/- 78 to 179 +/- 61 dyne.s/cm5 and pulmonary venous admixture (Qva/Qt) from 20.7 +/- 15.2 to 30.6 +/- 8.6 percent. Further analysis revealed that the magnitude of increased Qva/Qt was greater in patients who manifested septicemia (N = 10) compared to those who did not (N = 9): 12.3 vs 7.3 percent, respectively. We conclude that intravenous lipid administration was associated with increased MPAP and Qva/Qt in patients with ARDS, particularly when accompanied by septicemia. Although these alterations resolved after the lipid infusion was terminated, we suggest that prudent measures should be taken to guarantee adequate oxygenation during intravenous fat emulsion therapy in patients suffering from ARDS.