In four adult patients with late-stage acute respiratory distress syndrome (ARDS), a single dose of the artificial surfactant ALEC was given by intrabronchial instillation. There was no sustained clinical improvement, but bronchoalveolar lavage measurements indicated that phosphatidylcholine (PC) at 24 h after treatment had increased up to 4.4 fold and phosphatidylglycerol up to 34.7 fold. However, PC relative to total phospholipid remained below normal, and protein contamination relative to PC remained above normal. Thus, therapeutic formulations and regimens to achieve greater and more sustained supplementation of PC may be required in patients with late-stage ARDS.