The artificial pit technique has been used to study the electrochemistry of the pitting corrosion of 18 percent chromium-8 percent nickel stainless steel in ferric chloride solutions. Pitting corrosion has been observed to be a highly complex, time-dependent phenomenon. The concepts of polarization and electrochemical control must be modified when applied to pitting attack. A new concept of electrochemical action during pitting based on the mixed potential theory, has been proposed.