The diazepam withdrawal syndrome was studied in 10 patients who had abused the drug for 3 to 14 years. In the previous 6 months their consumption of diazepam had ranged from 60 to 120 mg daily; none had used other drugs during this period. The withdrawal period lasted about 6 weeks. The intensity of the symptoms and signs was high initially, fell during the first 2 weeks, then rose again in the third week, before finally declining. Three groups of symptoms and signs were identified. Group A symptoms occurred throughout withdrawal and included tremor, anorexia, insomnia and myoclonus. Group B symptoms and signs were largely confined to the first 10 days and were those of a toxic psychosis. Group C symptoms reached a peak in the third and fourth weeks of withdrawal and were characterized by sense perceptions that were either heightened or lowered. The symptom groups, the presence of tremor and myoclonus, and the relief of symptoms by a test dose permit diazepam withdrawal to be distinguished from anxiety. The biphasic course of the symptoms is probably related to the pharmacokinetics of diazepam.