Psychotropic drugs are widely prescribed and tend to be used on a long-term basis. The barbiturates are known to induce tolerance and dependence, with a well-defined and often severe withdrawal syndrome from high doses. By contrast, the benzodiazepines are infrequently associated with tolerance and dependence at high doses. Recent work, however, has suggested that a definite withdrawal syndrome can supervene on discontinuation of long-term normal doses of benzodiazepines. In view of the widespread and chronic use of the benzodiazepines, this may represent a major problem. The theoretical implications of such normal-dose dependence are discussed.