Chronic idiopathic urticaria (CIU) is a troublesome disorder with anunknown etiological agent. Mast cell activation and release of mediators occurin all forms of urticaria. Although histamine is the principal inflammatorymediator of mast cell derivation, other mediators are freed after mast cellactivation such as cysteinyl leukotrienes (leukotrienes C4, D4, and E4).1 We evaluatethe efficacy and tolerability of an antileukotriene drug, montelukast sodium,2 in relation to fexofenadine hydrochloride, an antihistaminicdrug, in patients affected by CIU.