In the past 25 y electrochemical techniques have been utilized in a variety of programmes designed to produce alloys of superior corrosion resistance to specific environments. The potentio-dynamic polarization technique gives unique information on the passivation properties of steels. The data obtained from the above technique, however, can be subject to error if specific precautions are not taken in the experimental procedure. This paper describes the results of an investigation on the influence of cathodic pretreatment on the anodic-dissolution kinetics of AISI Types 430 and 304 stainless steel in dilute H 2SO 4. Laboratory tests on Type 304 stainless steel have shown that prolonged exposure to cathodic hydrogen evolution increases the magnitude of the critical anodic c.d. Also, cathodic pretreatment produces a passive current maxima, the amplitude of which is related to the duration of the cathodic pretreatment. The magnitude of the effect is markedly different on ferritic steels compared with austenitic steels, being greater for the ferritic steels because of the higher diffusivity of hydrogen in a body-centered cubic lattice. These data show that previous theories about the cause of passive current maxima, such as carbide precipitation following a sensitizing heat treatment, or Ni enrichment, are in error.