Leukotriene C-4 is a potent mediator of allergic and inflammatory reactions, and is formed from arachidonic acid and glutathione through the sequential action of 5-lipoxygenase and leukotriene C-4 synthase (LTCS). These enzymes are predominantly expressed in cells of myeloid lineage. In this report, we have investigated LTCS mRNA expression in mouse brain. Expression was demonstrated using RT-PCR and RNase protection assays. In situ hybridization experiments showed exclusive staining of the choroid plexus of all brain ventricles. This expression pattern may provide a mechanism for the generation of LTC4 on the cerebral side of the bloodbrain barrier and suggests a possible novel regulator function of LTC4 in the formation of cerebrospinal fluid. (C) 2003 Elsevier Inc. All rights reserved.