Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), causes uncoupling of NOS leading to generation of reactive nitrogen species such as peroxynitrite. The lung generates a significant amount of ADMA, potentially contributing to plasma ADMA levels that have been related to endothelial dysfunction. ADMA infusion causes increased collagen deposition in lungs, suggesting that it could influence the development of chronic lung diseases such as fibrosis, COPD, and asthma. To explore the link between endogenous ADMA and asthma, we determined the levels of ADMA, enzymes implicated in its metabolism and peroxynitrite in murine models of allergic airway inflammation (AAI) resembling asthma. ADMA levels and nitrosative stress were found to be positively correlated in cytosol and mitochondria during AAI. This was associated with increased expression of protein-arginine methyltransferase 2 (PRMT2), an ADMA synthesizing enzyme; and reduced expression of dimethylarginine dimethylaminohydrolase (DDAH-2), an ADMA degrading enzyme, in bronchial epithelia. Increased nitrotyrosine similarly localized to the bronchial epithelium, as well as in infiltrated inflammatory cells. Administration of L-arginine that was expected to compete with ADMA and reverse the uncoupling/inhibition of NOS, restored normal ADMA metabolism along with the expected reduction of nitrosative stress in lung. Since DDAH2 function is known to be negatively related to oxidative stress, this may represent a feed forward loop effect. We conclude that a delicate balance between ADMA metabolizing enzymes is disturbed in bronchial epithelium during AAI, potentially causing increased nitrosative stress in a self propagating cycle. This represents a potential therapeutic target in asthma.