The cysteinyl leukotrienes LTC4, LTD4, and LTE4 are important mediators of human bronchial asthma. Pharmacologic studies have determined that cysteinyl leukotrienes activate at least 2 receptors, the protein encoded by this gene and CYSLTR2. This encoded receptor is a member of the superfamily of G protein-coupled receptors. Activation of this receptor by LTD4 results in contraction and proliferation of smooth muscle, oedema, eosinophil migration and damage to the mucus layer in the lung.