The concepts of dependence, addiction and abuse comprise overlapping clinical phenomena. The earlier anxiolytic drugs, in particular the barbiturates, were prone to abuse, i.e., non-medical use, and to high-dose misuse. Their modern counterparts, the benzodiazepines, are abused in a patchy way and are sometimes taken in regularly high doses. However, the main problem is physical dependence as manifested by a withdrawal syndrome on discontinuation of the drug. The withdrawal syndrome has been carefully described and comprises physical and psychological features. In particular, perceptual symptoms such as photophobia, hyperacusis and feelings of unsteadiness may predominate. The syndrome may come on during dosage reduction but generally starts 2-10 days after cessation of the benzodiazepine, depending on its elimination half-life. About a third of long-term users suffer a recognisable syndrome even after a tapered withdrawal, its duration usually being only a few weeks. A few patients go on to a prolonged withdrawal syndrome, often characterised by muscular spasm. The treatment of the withdrawal syndrome is supportive and non-specific. A few patients started on benzodiazepine therapy escalate the dose. They tend to show the characteristic 'passive-dependent' personality features and may previously have misused other CNS depressants such as the barbiturates and alcohol. Abuse of benzodiazepines occurs in a rather varied way from country to country. Worldwide, flunitrazepam has caused concern but, in the UK, the main problem has been the intravenous use of temazepam. The molecular pharmacology of the benzodiazepine receptor has been extensively studied and is undoubtedly complex.(ABSTRACT TRUNCATED AT 250 WORDS)