Laboratory studies of cocaine-exposed rodents, and positron emission tomographic studies of human cocaine abusers have suggested that chronic cocaine abuse downregulates dopaminergic function in the basal ganglia. The present study sought to provide behavioral evidence for this phenomenon by demonstrating enhanced levels of resting hand tremor among patients with previous histories of cocaine dependence. to determine the specificity of the phenomenon, patients with previous histories of alcohol dependence, cocaine/alcohol codependence, and cocaine/opiate codependence were also evaluated. Patients were assigned to one of four groups according to DSM-IIIR diagnostic criteria: (1) cocaine dependent (n = 19); (2) cocaine and alcohol dependent (n = 12); (3) cocaine and opiate dependent (n = 7); (4) alcohol dependent (n = 9). All were abstinent from their primary drug of abuse for a period of 1 to 5 months. The three patient groups with histories of cocaine dependence exhibited significantly more resting hand tremor than the alcohol-dependent and normal control groups. Furthermore, hand tremor in the former three groups was positively related to the number of self-reported uses of cocaine and negatively related to the number of months of cocaine abstinence.