We have been interested in understanding the mechanisms regulating the inflammatory process underlying acute lung injury. The current studies have employed a model of acute lung inflammation in mice triggered by bacterial lipopolysaccharide. The development of this injury was associated with increased expression of the chemokines, MIP-1α and MIP-2, that coordinate recruitment of neutrophils to the lung. IL-10 is a potent, endogenous anti-inflammatory molecule that has been shown to decrease lung inflammation partly on the basis of TNF-α and IL-1β inhibition. In these studies we tested the hypothesis that endogenous IL-10 modulates chemokine expression using the IL-10 knock-out mouse, and then explored the molecular mechanisms by which IL-10 might do so. The results demonstrate that significant elevations in both chemokines were observed in the absence of IL-10 and that these findings were associated with significant increases in lung neutrophil accumulation. In vitro studies defined two, gene-specific, mechanisms by which IL-10 regulated chemokine expression: mRNA destabilization and NF-κB inhibition. These results suggested that IL-10 is an important, endogenous regulator of chemokine expression in acute lung inflammation.