Since the discovery of opioid peptides, the brain opioid system has been implicated in the pathophysiology of a spectrum of mental disorders, including depression and epilepsy. For example, a growing body of evidence demonstrates that these neuropeptides are activated by seizures. Specifically, using electroconvulsive shock, it has been possible to describe an array of antinociceptive, autonomie, behavioral, biochemical, and electroencephalographic responses that appear to be mediated by endogenously activated opioids. A primary role for opioid peptides as neuromodulators of postictal seizure arrest and refractoriness is now recognized, and the existence in the central nervous sytem (CNS) of an endogenous anticonvulsant substance activated by electroconvulsive shock (ECS) has been determined. This review focuses on the more recent developments regarding ECS-induced modulation of brain opioid systems. The ability of ECS to alter opioid receptors, to influence the release and biosynthesis of the various opioid peptides, and to activate endogenous anticonvulsant mechanisms will be addressed.