A study was conducted on the amount, composition, surface properties, and subfraction distribution of surfactant phospholipids (PL) found on the alveolar surface of rats exposed to hyperoxic conditions. Male Sprague-Dawley-rats were continuously exposed to above 95% oxygen (7782447) (O2) for 64 hours; control rats were exposed to air. Following exposure, control and exposed rats were killed and alveolar lavage materials were collected by tracheal lavage. The lungs and trachea were removed for histopathological analysis. Measurements of PL and protein levels were conducted on the supernatant and pellet samples obtained from centrifugation. Determinations of the association between surface tension and surface area were made with a surfactometer. Subfractions of alveolar lavage materials were obtained by differential centrifugation for measurements of PL and disaturated phosphatidylcholine (DSPC) levels. The lungs from the O2 exposed rats were observed to increase 50% in wet lung weight as compared to the controls. The level of protein found in the alveolar lavage materials was increased by five to eight fold in O2 exposed rats. Changes in the alveolar lavage PL level and composition were also observed. The amount of total PL in O2 exposed rats were increased by 2.6 fold when expressed in terms of dry lung weight. While no significant trends were observed for individual PLs, DSPC levels were reduced from 46 to 39% after exposure to O2. The calculation of a stability index for alveolar lavage fluid samples revealed a 40% decrease in those from O2 exposed rats. Differential centrifugation indicated changes in the distribution of PL in alveolar lavage material subfractions. The majority of DSPC (72%) was found in the heavier subfractions from O2 exposed rats. Despite the greater amounts of surfactant on the alveolar surface of rats exposed to hyperoxic conditions, the authors conclude that the surface properties of the surfactant are impaired, possibly from the reduction of DSPC levels, increased amount of protein, and changes in the physical form.