Pieces of rat brain incubated in oxygenated Tyrode solution were stimulated with the divalent cation ionophore A 23187. Incubation media were assayed for leukotriene (LT) C4-like immunoreactivity as well as for prostaglandin (PG) D2, 6-keto-PGF1 alpha and thromboxane (TX) B2 using specific and sensitive radioimmunoassays. Spontaneous release of the cyclooxygenase products but only of trace amounts of LTC4-like immunoreactivity was detected. Stimulation with ionophore A 23187 increased the level of cyclooxygenase products and to a smaller extent the level of LTC4-like immunoreactivity. Inhibition of cyclooxygenase by indomethacin was paralleled by a significantly increased release of LTC4-like material under basal conditions as well as in the presence of ionophore A 23187. On the other hand, the synthesis of LTC4-like material was significantly decreased by the lipoxygenase inhibitors quercetin and nordihydroguaiaretic acid. The presence of LT-like material in rat brain incubates was confirmed by bioassay. The capacity of brain tissue to synthesize LT-like material may be important for cerebral blood flow as well as cellular functions in the central nervous system.