An extensive study was carried out on the release of different contaminants from cement stabilized wastes. The goal of the work was to make a computer code, called RECOSTA (RElease of COntaminant from cement STAbilized wastes), to support (i) the comprehension of the chemical-physical phenomena which govern the leachability of various elements (to choose the best composition for the immobilization matrix) and (ii) the definition of the protocols for monitoring and controlling of the release of pollutants (which occurs when hazardous waste are disposed of in a landfill). To this end the following toxic elements, incorporated in different cement based systems, were leached according to ANSI/ANS 16.1: Cs(I), Cd(II), Co(II), Cu(II), Pb(II), Sr(II), Zn(II), Cr(III), Fe(III), Cr(VI).