Book excerpt: Acute respiratory distress syndrome (ARDS) is difficult to treat and has a mortalitly rate of 40-60%. During ARDS, cytokine levels in the lungs are elevated and patients are treated with hyperoxia and mechanical ventilaion. Alone, these three factors can cause lung injury but the combination is thought to worsen lung damage. Using an over-distension model of lung injury, I investigated the effect of excessive mechanical stretch on a monolayer of murine alveolar epithelial cells (MLE-12) treated with the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-α). Results show that monolayer damage, i.e., formation of cell-free areas, may begin as early as 30 minutes from the beginning of excessive stretch. Moreover, the cell-free area formation due to TNF-α and stretch together was 16% greater than the cell-free area formed due to either stimulus alone. Future studies are needed to elucidate the cause of this form of damage.