Tolerance and physical dependence, although important in the addicted state, cannot account for the central problem of addiction—relapse from the abstinent state. Psychologic conditioning theory offers more satisfactory explanations. Methadone programs are effective, it is proposed, not because addicts have any "biochemical need" for opiates, but for straightforward pharmacologic and psychologic reasons. Methadone hydrochloride abolishes the periodic withdrawal sickness experienced by the active addict. By producing cross-tolerance, it diminishes the rewarding (reinforcing) effects of heroin. Thus methadone allows the motivated addict to discontinue heroin use without discomfort. A methadone program should strengthen that motivation by providing a nonpunitive environment within which self-help and peer help can operate to alter life style. A methadone temporary support program is outlined, as an alternative to methadone maintenance of indefinite duration.