Characterization of some selected chemical and mineralogical components and the experiments aiming to limit Pb, Zn and Cd mobility Zn-Pb-metarullgical slag from the Mining and Metarullgical Company at Bukowno (Upper Silesia), have been carried out. The extent of heavy metals stabilization — using cement and/or fly ash — was tested by leaching with water and solutions of different pH. The contents of heavy metals studied in the initial samples of slag were as follows (wt. %).: Pb — 2.68; Zn — 3.25; Cd — 0.04. There were the following results of leaching tests (mg/dm³): Pb — 1.28; Zn < 0.02; Cd < 0.01; SO^2-₄ — 550; Cl^- — 7.3; F^-< 0.04; NO^-₃ < 0.1. It was found that concrentrations of Pb and SO^2-₄ released to the water from tested slag were higher than the levels permitted by the Polish ecological regulations of 0.5 and 500 mg/l, respectively. The best immobilization properties were shown by cement and cement with fly ash added into slag dump. Leaching tests showed a general rule: the more nitric acid added to the sample, the more metals were released to the solution. pH is the main factor controlling heavy metal mobility which, while pH decreases, significantly increases at pH below 8. Lead shows a different behaviour than Zn and Cd. Most of the lead was released from slag at pH below4.