The electrocatalytic activity of copper in base is of considerable importance in electroless copper deposition which in turn is of increasing importance in microfabrication technology. Glyoxylate is a far less hazardous reducing agent than formaldehyde for use in alkaline copper deposition baths and its electrocatalytic oxidation on copper in base was investigated. The results are in excellent agreement with the incipient hydrous oxide/adatom mediator (IHOAM) view of electrocatalysis at metal surfaces. The aldehyde functions as both an oxidant and a reductant whose reduction and oxidation appear to be mediated by active copper atoms and incipient hydrous oxide species. respectively. The changeover from one reaction to the other, at ca. -0.1 V (RHE) at 60 degrees C, was related to the redox transition of the interfacial mediator species which takes place at a potential that is within the double layer region of copper in base.