Tranquilizers, and specifically benzodiazepines (BZD), have become one of the most widely used group of drugs in the world; some have suggested too widely used. Interest in these drugs is still extremely high, both from the scientific and sociological point of vi ew. This is best documented by the fact that the present review is based on more than 700 articles published between 1981 and 1984 covering various aspects of clinical pharmacology. Pharmacodynamic studies are mostly concerned with effects of the drug on the central nervous system (CNS), as well as on behavious and neuroendocrine functions. The former include computer-assisted quantitative analyses of the scalp-recorded wake electroencephalogram (EEG), based on which it seems possible to determine if, how, when and at what dose a newly developed compound affects the human brain. Sleep investigations are now concerned not only with the effect of the drug on the all-night sleep, but also on the quality of awakening and early morning behaviour as well as with residual effects during daytime, affecting amnestic and cognitive functions, psychomotor performance (specifically in regard to driving ability), as well as mood and affectivity. Finally, for almost a decade increasing concern has been expressed about the widespread use of tranquillizers in society. Scientific evidence concerning thiss issue will be reviewed so that an appropriate medical decision may be reached for the treatment of the individual patients after consideration of the beneficial effects as well as undesirable side-effects.