Leukotrienes B4, C4, D4 and E4, together with five monohydroxyeicosatetraenoic acids, were isolated after incubation of chopped rat brain tissue with ionophore A23187. The monohydroxyeicosatetraenoic acids were 5-hydroxy-6,8,11,14-eicosatetraenoic acid, 9-hydroxy-5,7,11,14-eicosatetraenoic acid, 11-hydroxy-5,8,12,14-eicosatetraenoic acid, 12-hydroxy-5,8,10,14-eicosatetraenoic acid and 15-hydroxy-5,8,11,13-eicosatetraenoic acid. Identification of the compounds was performed using reversed-phase high-performance liquid chromatography, ultraviolet spectroscopy and gas chromatography-mass spectrometry. Formation of the compounds was inhibited by micromolar concentrations of nordihydroguaiaretic acid. Indomethacin specifically inhibited the formation of 11-hydroxy-5,8,12,14-eicosatetraenoic acid, suggesting that this compound was produced as a by-product during cyclooxygenase-catalyzed prostaglandin synthesis.