Ricinelaidicacid is a 12-hydroxy fatty acid and an antagonist of leukotriene B4 (LTB4) receptors (Ki = 2 μM in porcine neutrophil membranes). It inhibits chemotaxis and calcium flux induced by LTB4 in isolated human neutrophils (IC50s = 10 and 7 μM, respectively). Ricinelaidicacid (1 mg/kg, i.v.) inhibits bronchoconstriction induced by LTB4 in rats by 46%.