The principal action of the sedative-hypnotic drugs, of whom the barbiturates are the most widely known and utilized, is to produce drowsiness and promote sleep. At one time these were also the only drugs available to calm seriously anxious or disturbed people. Unfortunately, in addition to their clinical applications these drugs manifest a very high abuse potential. Experienced drug abusers report feelings of well-being and euphoria while under the influence of these drugs. Self-administration experiments conducted in animals have shown that the barbiturates are potent reinforcing agents. In controlled studies in humans, former drug abusers express a preference for barbiturates over benzodiazepines and will "work" to receive barbiturates. Long term consumption of the sedative-hypnotics, particularly barbiturates, leads to dependence characterized by a severe, potentially life-threatening abstinence syndrome following the abrupt withdrawal of the drug. Withdrawal manifestations include delirium and grand mal seizures. Because of the high abuse potential of these drugs, their manufacture and distribution has been greatly curtailed, and for most clinical applications they have been largely replaced by drugs, e.g., the benzodiazepines, which appear to have much less abuse liability.