Cellular injury during tissue hypoxia is due, in part, to reactive intermediates released by activated leukocytes. We found that the inflammatory mediators tumor necrosis factor (TNF)-alpha, IL-6, and IL-1beta are elevated in situ in lung macrophages on day 14 following exposure of rats to intermittent or chronic hypoxia from birth. Because inflammatory mediators can increase lipolysis in adipocytes, we also measured serum unbound free fatty acids (FFAu)--the biologically active compartment of FFA--in rat pups exposed to intermittent or chronic hypoxia. FFAu values were markedly elevated during the first 2 days of life in all rats, displaying an approximately 3-fold decrease from day 2 to day 3. Exposure to chronic hypoxia significantly increased FFAu levels measured on day 13. Since elevated serum FFAu are known to suppress leukocyte activation, we speculate that increased FFAu levels represent a mechanism for attenuating inflammation and tissue injury following sublethal hypoxia in the perinatal period, either physiologically in the immediate newborn period, or as a late response to ongoing hypoxic insult.