The stabilization of toxic metals (Cd, Zn, Pb, Cu and Mn) in a solid waste from a zinc refinery was studied by the addition of either a synthetic adsorbent (zeolite A) or an organic adsorbent (dried water hyacinth and rice hull carbon). The stabilization ability of an adsorbent was evaluated by means of sequential extraction, which separated the metals into five fractions. Metals extracted in the first two fractions by relatively weak solvents are considered as mobile. These metal contents provide an estimation of the amount available for plant uptake. Metals extracted in the last three fractions are considered to be immobile. Stabilization ability of an adsorbent when mixed with solid waste can be considered as the transformation of a metal from mobile to immobile form.