A prostaglandin F2-like compound, 8-epi-PGF2alpha, formed from oxidation of arachidonate, has been proposed as an indicator of lipid peroxidation. We determined whether tracheal aspirate or urinary 8-epi-PGF2alpha levels would differ over time or between infants in a control group and infants with severe respiratory failure. We correlated tracheal aspirate 8-epi-PGF2alpha levels with the fraction of inspired oxygen and with mean airway pressures at 24 and 48 hours of life. Levels in tracheal aspirates were in the range of 0 to 36 pg/microg of fSC of IgA and were higher in infants with severe pulmonary disorders compared with those in infants in the control group (p < 0.02). Urinary concentrations did not discriminate between sick infants and infants in the control group.