This review focuses on finding neurochemical changes in physical dependence on butorphanol, a relatively potent mixed agonist-antagonist opioid analgesic agent that is five times more potent than morphine in antinociceptive effects. The chronic administration of butorphanol induces physical dependence. Withdrawal from such dependence can be reliably precipitated by administration of a narcotic antagonist, e.g., naloxone. Evidence for critical involvement of excitatory aminoacid (glutamate), opioid receptors, and phosphorylation of proteins in these phenomena is summarized.