(±)5-HETE lactone is a cyclic ester formed by acid-catalyzed nucleophilic addition of the C-5 hydroxyl to the C-1 carboxyl of (±)5-HETE. (±)5-HETE lactone is an inhibitor of 5-LO from rat basophilic leukemia cells with an IC50 of 27 μM. The lactone is several times more potent than the linear (±)5-HETE.{690}