Leukotriene B4 (LTB4) and the cysteinyl-leukotrienes LTC4, LTD4 and LTE4 are potent proinflammatory mediators derived from arachidonic acid through the 5- lipoxygenase pathway. They are secreted from eosinophils and other inflammatory cells such as mast cells and macrophages. The primary action of leukotrienes includes contraction of human airway muscle, chemotaxis, and increased vascular permeability, with secondary effects of inhibiting allergen-induced early and late responses. Several in vivo and in vitro studies suggest a role for cysteinyl leukotrienes in the pathogenesis of atopic dermatitis and there is a rationale for the use of pharmacological agents to antagonize their effects in the treatment of atopic dermatitis. Levels of LTE4 measured in urine (Urinary-LTE4) may be a useful measure of whole-body cysteinyl-leukotriene production in vivo, because that LTE4 is a stable urinary metabolite of LTC4 and LTD4. Urinary-LTE4 has been measured in individuals with atopic dermatitis, but in small-scale studies, and the results are conflicting.