The aim of this study was to determine the concentration of zinc, copper and magnesium in the blood serum of drug addicts in order to ascertain whether drug abuse has an effect on the concentration of these metals. The study was carried out on a group of 33 addicts undergoing treatment at the Department of Clinical Toxicology, Collegium Medicum, Jagiellonian University in Kraków. The control group consisted of 22 young, healthy, drug free, male volunteers. Analyses were performed using flame atomic absorption spectrometry. The results demonstrate that zinc serum concentrations in the examined group of addicts before therapy (mean 0.82 mg/l) were reduced in relation to the control group (mean 1.12 mg/l), and was slightly enhanced after the detoxification process (mean 0.86 mg/l). The opposite effect was observed in the case copper serum concentration. The copper level in the group of addicts on admission to hospital (mean 1.35 mg/l) increased in relation to the control group (mean 1.11 mg/l) and was lower during hospitalisation (mean 1.18 mg/l). The concentration of magnesium in the serum of drug addicts did not change during therapy and was in the same range as in the control group (mean concentrations were 20.3 mg/l, 20.2 mg/l and 20.6 mg/l respectively).