Inhibitors which affect the reaction of iron with hydrochloric acid differ in the mechanism of their action. They increase the metal‐solution overvoltage only slightly, but considerably raise the hydrogen overvoltage. Inhibitors, otherwise effective, have little influence on the reduction of ferric ions at a platinum cathode. At an iron cathode, ferric ions are reduced primarily by hydrogen, which inhibitors activate. Inhibitors are effective in the dissolution of iron only if the reaction takes place. This explains the relatively slight effect of inhibitors on the dissolution of iron in the presence of oxygen.