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Allergens elicit host production of mediators acting on G-protein–coupled receptors to regulate airway tone. Among these is prostaglandin E2 (PGE2), which, in addition to its role as a bronchodilator, has anti-inflammatory actions. Some patients with asthma develop bronchospasm after the ingestion of aspirin and other nonsteroidal anti-inflammatory drugs, a disorder termed aspirin-exacerbated respiratory disease. This condition may result in part from abnormal dependence on the bronchoprotective actions of PGE2. We sought to understand the functions of regulator of G protein signaling 4 (RGS4), a cytoplasmic protein expressed in airway smooth muscle and bronchial epithelium that regulates the activity of G-protein–coupled receptors, in asthma. We examined RGS4 expression in human lung biopsies by immunohistochemistry. We assessed airways hyperresponsiveness (AHR) and lung inflammation in germline and airway smooth muscle–specific Rgs4 −/− mice and in mice treated with an RGS4 antagonist after challenge with Aspergillus fumigatus. We examined the role of RGS4 in nonsteroidal anti-inflammatory drug–associated bronchoconstriction by challenging aspirin-exacerbated respiratory disease–like (ptges1 −/− ) mice with aspirin. RGS4 expression in respiratory epithelium is increased in subjects with severe asthma. Allergen-induced AHR was unexpectedly diminished in Rgs4 −/− mice, a finding associated with increased airway PGE2 levels. RGS4 modulated allergen-induced PGE2 secretion in human bronchial epithelial cells and prostanoid-dependent bronchodilation. The RGS4 antagonist CCG203769 attenuated AHR induced by allergen or aspirin challenge of wild-type or ptges1 −/− mice, respectively, in association with increased airway PGE2 levels. RGS4 may contribute to the development of AHR by reducing airway PGE2 biosynthesis in allergen- and aspirin-induced asthma. [ABSTRACT FROM AUTHOR]