The noxious potential of metallurgical tailings from the Ag/Pb/Zn/Cu mining district of Sta. María de la Paz (Mexico) is ascertained via the chemical characterization of slag material. Batch experiments using various extraction solutions (e.g. natural rainwater, water rich in humic substances, ammonium nitrate solution) revealed information on the dissolution behaviour of the elements Fe, Mn, Ni, Cu, Zn, As, Ba and Pb from slag with respect of grain size (slag material screened under 2 mm and analytically fine fraction) and elution time (2, 7.5, 24 and 240 h). An initial ecotoxicological assessment of the results is made and the environmental danger caused by large volumes of slag tailings is discussed.