The retinoid-related orphan receptor α (RORα), a member of the ROR subfamily of nuclear receptors, has been implicated in the control of a number of physiological processes, including the regulation of several immune functions. To study the potential role of RORα in the regulation of innate immune responses in vivo, we analyzed the induction of airway inflammation in response to lipopolysaccharide (LPS) challenge in wild-type and staggerer (RORαsg/sg) mice, a natural mutant strain lacking RORα expression. Examination of hematoxylin and eosin-stained lung sections showed that RORαsg/sg mice displayed a higher degree of LPS-induced inflammation than wild-type mice. Bronchoalveolar lavage (BAL) was performed at 3, 16, and 24 h after LPS exposure to monitor the increase in inflammatory cells and the level of several cytokines/chemokines. The increased susceptibility of RORαsg/sg mice to LPS-induced airway inflammation correlated with a higher number of total cells and neutrophils in BAL fluids from LPS-treated RORαsg/sg mice compared with those from LPS-treated wild-type mice. In addition, IL-1β, IL-6, and macrophage inflammatory protein-2 were appreciably more elevated in BAL fluids from LPS-treated RORαsg/sg mice compared with those from LPS-treated wild-type mice. The enhanced susceptibility of RORαsg/sg mice appeared not to be due to a repression of IκBα expression. Our observations indicate that RORαsg/sg mice are more susceptible to LPS-induced airway inflammation and are in agreement with the hypothesis that RORa functions as a negative regulator of LPS-induced inflammatory responses.