The sulfur isotope composition of 36 sulfide minerals, separated from the ilvaite and the hedenbergite zones of the replacement skarn-sulfide deposit in lower Liassic marble associated with Pliocene igneous rocks of Valle del Temperino, is fairly uniform: delta 34 S = 8.73 + or - 0.11 per mil for pyrite, 8.87 + or - 0.44 per mil for sphalerite, 8.19 + or - 0.61 per mil for pyrrhotite, 8.35 + or - 0.54 per mil for chalcopyrite, and 7.73 + or - 1.22 per mil for galena.The isotopic data and the iron content of sphalerite, together with geological and mineralogical evidence, indicate a shallow emplacement of the mineralization and a multistage depositional process developed at decreasing temperatures from about 400 degrees down to 250 degrees C according to fluctuations of the physicochemical parameters. These fluctuations appear to be restricted to an f (sub O 2 ) -- pH field where H 2 S and HS (super -) were the prevailing sulfur aqueous species. A delta 34 S (sub Sigma S) = 8 per mil was estimated for the total sulfur in the ore-forming fluids. The sources of sulfur for the Valle del Temperino deposit may have been sulfate (delta 34 S = 12 / 14.6ppm) and/or sulfide (delta 34 S = 5 / 12ppm) associated with the Triassic-Paleozoic(?) formations Calcare Cavernoso and Filladi di Boccheggiano of Tuscany.