The role of thiosulfates in pitting induced by chlorides on Fe-17Cr alloys in neutral medium was investigated by electrochemical and XPS techniques. The concentration was 30 ppm S2O32− in 0.02 M NaCl. The studied alloys contained different contents and kinds of sulfide inclusions (Ti or Mn sulfldes). Electrochemical experiments (i-E curves and pitting probability measurements) show the deleterious effect of thiosulfate addition. The detrimental effect of the thiosulfates on the pitting resistance increases with increasing sulfur content in the alloy. The Ti-stabilized alloy exhibits a better pitting resistance than the Nb-stabilized alloys. For the XPS study, an ultra-pure Fe-17Cr alloy was used. The XPS study was performed after (a) immersion of the alloy (cleaned by argon sputtering) in the solution 0.02 M NaCl + 30 ppm S2O32− and (b) addition of the thiosulfates after passivation in 0.02 M NaCl. The XPS results give the evidence that the thiosulfates are reduced on the metallic surface whereas they do not interact strongly with the passive film surface. Sulfide islands are formed at the bare alloy surface and prevent repassivation.