Several tons of slag are present at the lead-silver smelting sites at Laurion. Samples were taken and subjected to quantitative, x-ray fluorescence and x-ray diffraction analyses. The slag is characterized by high CaO and lead content. The mean values of various component metals are given. The most widely recurring mineral present is hedenbergite (CaFe(Si₂O₆)). Chemical and phase composition of the slag reflect the composition of the ores and the con ditions of the smelting process. Argentiferous galena with traces of secondary ores such as cerassite was subject to a roasting-reduction reaction to obtain argentiferous lead, which in turn was converted to silver by cupellation. To economize on charcoal used during the smelting process, high lead residues were accepted; the weight ratio of ore to fuel is given. The productivity of the smelter during the 5th-4th century B.C. is indicated. See also AATA 17-720. -- AATA