Landfilling of ash from waste‐to‐energy conversion plants poses a potential problem because some ashes contain excessive concentrations of Cd and Pb according to the Extraction Procedure test (EP toxicity test) developed by the Environmental Protection Agency (EPA). Current EPA limits to delineate hazardous materials are 1.0 and 5.0 μg/mL of Cd and Pb, respectively, in the 0.5Macetic acid extract. Since incinerator residues from several facilities have been reported to exceed these levels, a study was initiated whereby ash was combined with different amendments in an attempt to reduce Cd and Pb solubility below EPA limits and to render the ash acceptable for landfilling. Amendments most effective in reducing Pb solubility and extractability by the EP test were: CaO; commercial calcitic lime—CaCO3; limestone scrubber sludge (LSS) from a coal‐fired steam plant; fluidized bed waste (FBW) from a coal‐fired steam plant; acidic NH4H2PO4and basic K2HPO4; and elemental S. Cadmium solubility was reduced only by CaO and the phosphate sources.