We followed the magnesium effect (Magne B(6)R, Sanofi-Synthelabo) with internal administration in 53 adult neurotic smoking patients (more than 10 cigarettes/day) of both genders admitted into psychiatric hospital. The nicotine dependence was assessed by the Fagerstrom test, initially and after 28 days of magnesium intake. Plasmatic magnesium level was determined before any therapy and at 28 days. All patients received benzodiazepines during the trial. Our data show that patients that received magnesium therapy showed a significant decrease in the number of cigarettes smoked and Fagerstrom test after 4 weeks [Fagerstrom score 7.93 +/- 0.17 before magnesium therapy versus 6.78 +/- 0.18 (P < 0.05) after 28 days of magnesium therapy]. In the group of smokers who did not receive magnesium, the Fagerstrom score did not change significantly [Fagerstrom score 7.48 +/- 0.22 initial versus 7.24 +/- 0.19 after 28 days]. Magnesium supplementation raised plasmatic levels (17.2 +/- 1.2 mg/L before versus 26.1 +/- 1.6 mg/L after 28 days of magnesium intake, P < 0.01). The results suggest that this cation might be a useful adjuvant in treatment of nicotine pharmacodependence.