In situ measurements of salt layers were made during localized corrosion to determine if Mo additions improved localized corrosion resistance of stainless steels by forming a Mo-rich salt layer. A high intensity 8 mu m diameter polychromatic x-ray beam and an energy dispersive x-ray detector were used to analyze the distribution of the dissolved steel components at the stainless steel/solution interface. Relative to the steel composition, the salt layer was high in iron with lower fractions of other metal ions. Only a small fraction of molybdenum was present, negating suggestions that a Mo salt inhibited corrosion.