Metal sulfide oxidation is important in many geochemical environments especially in the formation of acid mine drainage (AMD) and the environmental problems associated with it. Understanding metal sulfide oxidation pathways may assist in the development of remediation strategies for AMD impacted sites. The stable sulfur and oxygen isotopic composition of secondary sulfates resulting from metal sulfide oxidation may allow determination of the dominate oxidation pathway (i.e. abiotic or biotic, aerobic vs. anaerobic). Bacteria, such as Thiobacillus ferrooxidans, can play a significant role in the weathering and oxidation of sulfide minerals. To properly interperet the isotopic composition of sulfate produced at AMD sites, microbiological oxidation processes must be better understood. Despite previous work done in this area, there are still many fundamental questions related to the stable isotope geochemistry of metal sulfide oxidation; this is especially true for microbiological pathways. We are determining the oxygen and sulfur isotope ratios of sulfate from field and laboratory experiments to elucidate oxidation pathways during metal sulfide oxidation. In the laboratory, various metal sulfides (pyrite, galena, sphalerite ) have been reacted in biological (T. ferrooxidans) and abiotic oxidation experiments, which will eventually facilitate the interpretation of the isotopic composition of secondary sulfate from AMD sites.