Leukotrienes (LTs) are a group of acute inflammatory mediators derived from arachidonic acid via the 5-lipoxygenase (5-LO) pathway in leukocytes. LTC4, LTD4, and LTE4 are collectively referred to as cysteinyl leukotrienes (CysLTs). LTC4 and LTD4 are potent mediators of asthma and hypersensitivity. They induce bronchoconstriction, increase microvascular permeability, and are vasoconstrictors of coronary arteries. The biological activity of LTE4 is much lower in most systems studied, but its presence reflects the prior existence of LTC4 and LTD4. Cayman’s CysLT Express ELISA Kit is a competitive assay that can be used for measurement of all three primary CysLTs in urine, culture media, and other sample matrices. The assay has a range from 7.8-1,000 pg/ml and a sensitivity (80% B/B0) value of approximately 20 pg/ml. This sensitive assay takes about three hours to complete.