Cathodic inhibition effects of nickel and iron ions on the proton reduction reaction are demonstrated in chloride, sulfate, and perchlorate solutions. They are not caused by metal hydrolysis but are induced electrochemically and linked to the anomalous codeposition of NiFe alloys. The addition of zinc ions to a nickel electrolyte also inhibits the reduction of protons and nickel ions, but this effect is not caused by an electrochemical reaction. Therefore it is suggested that the anomalous codeposition of ZnNi proceeds via a different mechanism than the anomalous electrodeposition of NiFe.