The presence of binding sites for leukotriene C4 (LTC4) is demonstrated in the mouse forebrain, by using autoradiography of sections incubated with tritiated LTC4. The binding of LTC4 is inhibited by an excess of cold LTC4, but unaffected by the presence of a large excess of LTD4, which differs from LTC4 by the absence of a glutamic acid residue. The density of binding sites is minimal on fiber bundles and on choroid plexuses, maximal at the level of granule cell-rich structures such as the dentate gyrus and entorhinal area, and high in the cerebral cortex, thalamic relay nuclei and the caudoputamen. These data suggest that leukotrienes and their receptors might play a role as regulators of central neural activity, a hypothesis which was recently proposed by Lindgren et al.