We studied the effects of oxygen concentrations (21 to 50%) considered clinically "safe" on clearance of inhaled technetium-labeled diethylene triamine pentaacetate (99mTc DTPA) and the concentration of albumin in bronchoalveolar lavage (BAL) fluid of normal subjects. We also measured several markers of cell injury and inflammation in the BAL fluid including total and differential cell counts, lactate dehydrogenase, alkaline phosphatase, extracellular potassium, and several eicosanoids. Subjects inhaled oxygen (50, 40, 30, or 21%) for a mean of 45 h; there were no symptoms or bronchoscopic signs of oxygen toxicity. The concentration of albumin in BAL fluid was increased compared with baseline measurements in a dose-dependent manner in subjects exposed to 30% oxygen and above. Clearance of 99mTc DTPA was increased only in subjects who inhaled 50% oxygen. There were no significant changes in BAL fluid volume or total and differential cell counts after oxygen exposure. A trend towards an increased percentage of polymorphonuclear leukocytes was noted in the 50% oxygen group. We found no evidence of cell injury or inflammation in the BAL fluid. Supplemental humidity did not appear to influence the findings in the 50% oxygen group. Thus, oxygen in concentrations considered clinically "safe" increases clearance of 99mTc DTPA and BAL albumin concentration in normal subjects after a relatively short time of exposure.