We studied trace elements (zinc, copper, magnesium, iron, and lithium) by atomic absorption spectrophotometry in the plasma and erythrocytes of 120 subjects: 20 healthy controls and 100 parenteral drug addicts (69 heroin and 31 heroin + other drugs). Plasma Zn and intraerythrocytic Zn and Fe were decreased, whereas plasma and intraerythrocytic Cu were significantly increased in the group of drug addicts with respect to the healthy controls. Moreover, a period of abstinence longer than 10 days was associated with lower plasma levels of Zn and Li in subjects who had taken drugs shortly before they were examined. The presence of serological markers against HBV and HIV did not seem to influence the behavior of the trace elements in blood.