Prior research on growth of corrosion pits have shown that the metastable pits repassivate due to the rupture of the oxide pit cover and mixing of the bulk solution with pit solution. Stable pit growth only occurs if the metastable pits stabilize. Pitting typically is related to the presence of chlorides but has also been seen in other anions like thiosulfates. Thiosulfate pitting tends to have lower pitting potentials as well as repassivation potentials than chloride pitting. In some environments such as paper machine white water thiosulfate and chloride ions may coexist. The relative roles of thiosulfate and chloride on metastable pitting of austenitics stainless steels as well as duplex stainless steels are not clear. In this study we investigate the effect of thiosulfate on metastable pitting in chloride containing solution using potentiostatic polarization. Pit morphology is characterized using optical and scanning electron microscopes.