Converts hepoxilin A3 into trioxilin A3. Highly specific for the substrate, having only slight activity with other epoxides such as leukotriene A4 and styrene oxide [2]. Hepoxilin A3 is an hydroxy-epoxide derivative of arachidonic acid that is formed via the 12-lipoxygenase pathway [2]. It is probable that this enzyme plays a modulatory role in inflammation, vascular physiology, systemic glucose metabolism and neurological function [4]. In vertebrates, five epoxide-hydrolase enzymes have been identified to date: EC 3.3.2.6 (leukotriene-A4 hydrolase), EC 3.3.2.7 (hepoxilin-epoxide hydrolase), EC 3.3.2.9 (microsomal epoxide hydrolase), EC 3.3.2.10 (soluble epoxide hydrolase) and EC 3.3.2.11 (cholesterol 5,6-oxide hydrolase) [3].