The cysteinyl leukotrienes (CysLTs) are lipid mediators that have been implicated in the pathogenesis of allergic diseases. Pharmacological studies using CysLTs indicate that there exist two classes of receptors named CysLT1 and CysLT2. The former is sensitive to CysLT1 receptor antagonists currently used for the treatment of asthma and allergic rhinitis. Our previous immunohistochemical and autoradiographic studies showed that anti-CysLT1 receptor antibody adhered to eosinophils, mast cells, macrophages, neutrophils, and vascular endothelial cells in human nasal mucosa, and that a novel radioactive CysLT1 receptor antagonist, [3H]-pranlukast, bound specifically to CysLT1 receptors in human inferior turbinate and its binding sites were localized to vascular endothelium and interstitial cells. These data suggest that in allergic rhinitis, the major targets of CysLT1 receptor antagonists are the vascular bed and infiltrating leucocytes such as mast cells, eosinophils, and macrophages. Clinical trials have demonstrated that CysLT1 receptor antagonists are as effective as antihistamines, but are less effective than intranasal steroids for the treatment of allergic rhinitis. The use of CysLT1 receptor antagonists in combination with antihistamines has generally resulted in greater efficacy than when these agents were used alone.