Arachidonic acid may be a major messenger controlling the electrical and biochemical behaviour of neurons and glial cells. Here we review the experiments which have brought about this notion. We outline how, and from which cells in the CNS, arachidonic acid is released. We then discuss the cellular effects of arachidonic acid and its derivatives, and whether the doses of arachidonic acid applied in physiological experiments are in any way comparable to the level of arachidonic acid generated by endogenous release mechanisms. Finally, we consider the role of arachidonic acid in the particular situations of long term potentiation of synaptic transmission, brain anoxia/ischemia and presynaptic inhibition. © 1993 Academic Press Limited.