Uric acid is a ubiquitous end product of purine metabolism in humans that is mainly excreted in urine, whereas in other mammals it is further metabolized to allantoin by uricase. The final two steps in its production are catalyzed by xanthine oxidase, which generates superoxide. Uric acid acts as a potent peroxynitrite scavenger and antioxidant. However, high levels of serum uric acid (>120 µg/ml), termed hyperuricemia, are associated with gout, kidney stones, metabolic syndrome, hypertension, renal disease, and cardiovascular disease. Uric acid in the form of monosodium urate crystals has been proposed to trigger interleukin-1β-mediated inflammation by activating the NOD-like receptor protein 3 inflammasome.