Electrochemical polarization experiments in conjunction with surface analyses using ultrahigh vacuum transfer showed that the presence of S, above a certain threshold amount, accelerated the corrosion of Fe when polarized at a normally passive potential in 55 weight percent Ca(NO3)2 solution at 60-degrees-C. Above the threshold amount, the corrosion rate did not depend on the S content. During corrosion, much of the S remained in the corrosion product film, and a large portion of the charge passed contributed to film growth. Similiarities between the effects of S and those of P reported previously may help explain the similar influences of S and P as grain boundary impurities on the intergranular stress corrosion cracking of Fe.