The SHRIMP ion microprobe has been used to determine the relative sulfur isotopic compositions of pyrite, pyrrhotite, chalcopyrite, galena, sphalerite, and barite, employing a 10 kV, 3nA, negative oxygen primary ion beam and measuring positive secondary ions accelerated to 11 kV. Tests showed the minerals to be stable emitters of secondary ions, and intensities of the 32S + secondary ion beams ranged from 0.3 to 0.07 MHz in the order: sphalerite > pyrite > chalcopyrite > pyrrhotite > galena > barite, enabling measurement of 34S/ 32S ratios to a precision and accuracy near ±2 permil (2σ). Materials of diverse 34S concentration and/or matrix were repeatedly analyzed without detectable memory effect. Isotopic fractionation during analysis was mineral species-dependent and linear in terms of 32S, 33S, and 34S over a range in delta values of 60 permil, producing easily corrigible ratios and eliminating the need for standards isotopically similar to the samples. Fractionation varied from 1.5 to 6% u −1 in the order: galena < chalcopyrite < pyrrhotite = pyrite < barite and follows the relative bond strengths of the minerals. This apparently simple fractionation behavior suggests that, ultimately, it may be possible to reference all analyses to a single standard. Some irregularity in the fractionation of ratios from sphalerite, possibly related to matrix effects, has delayed its incorporation into this scheme.