Cysteinyl leukotrienes (CysLTs), slow-reacting substances of anaphylaxis, are lipid mediators known to possess potent proinflammatory action. Pharmacological studies using CysLTs indicate that at least two classes of G protein-coupled receptors (GPCRs), named CysLT₁ and CysLT₂, exist; the former is sensitive and the latter is resistant to the CysLT₁ antagonists currently used to treat asthma. Although the CysLT₁ receptor gene has been recently cloned, the molecular identity of the CysLT₂ receptor has remained elusive. Here we show that the pharmacological profile of an orphan GPCR (PSEC0146) is consistent with that of the CysLT₂ receptor. In human embryonic kidney 293 cells that express the PSEC0146 cDNA, leukotriene C₄ (LTC₄) and leukotriene D₄ (LTD₄) induce equal increases in intracellular calcium mobilization; these increases are not affected by CysLT₁ antagonists. Additionally, [³H]LTC₄ specifically binds to membranes from COS-1 cells transiently transfected with PSEC0146. Large amounts of the PSEC0146 mRNA are found in human heart, placenta, spleen, and peripheral blood leukocytes but not in the lung and the trachea. Pharmacological feature and expression studies will eventually lead to a better understanding of the classification of CysLT receptors, possibly leading to a reconsideration of the pathological and physiological role of CysLTs.