A hydroxide oscillation model has been proposed to account for the observed "nanolaminated" structure in electrodeposited Zn and Zn-Co alloys produced under potentiostatic control. At a critical cathode potential the Zn deposition proceeds in a cyclically changing environment arising from the regular formation and decay of a zinc hydroxide layer near the cathode surface, which produces Zn-ZnO laminations in the deposits. Co was found to enrich at the Zn-ZnO interface. Such a model is supported by evidence obtained from electrochemical measurements and transmission electron microscopy observations, and this has given some insight into the anomalous behavior of Zn-Co deposition.