Cysteinyl leukotrienes (CysLTs) mediate their biologic activities through interactions with the CysLT1 and CysLT2 receptors. CysLT1 receptors are prominently expressed on smooth muscle cells and lung fibroblasts, whereas CysLT2 receptors are expressed on heart Purkinje fiber cells, adrenal chromaffin cells, and endothelial cells. Both receptors are expressed on eosinophils and mast cells, but CysLT1 receptors alone are on neutrophils. Antigen-presenting cells more prominently express the type 2 receptor. CysLT1 receptors are uniquely important for bronchospasm, whereas CysLT2 receptors can stimulate endothelial cell adherence, myofibroblast proliferation, and chemokine production by mast cells. Comprehensive inhibition of the proinflammatory activities of CysLTs might require either combination CysLT1 and CysLT2 receptor antagonists or inhibitors of the CysLT synthesis pathway.