Eugenol dose-dependently inhibited 5-HETE (5-hydroxy-5, 8, 10, 14-eicosatetraenoic acid) and 15-HETE formation by human polymorphonuclear leucocytes. p-Chlorophenol, guaiacol and phenol also inhibited the lipoxygenases. Formation of HETEs by rat dental pulp was inhibited by eugenol and p-chlorophenol. The concentrations of the phenolics required to inhibit lipoxygenases were in the similar range with those used for inhibiting cyclooxygenase. These results showed that phenolic compounds inhibited lipoxygenases and thus suggest that these compounds may be dual inhibitors of lipoxygenase and cyclooxygenase.