In this work X-ray photoelectron spectroscopy studies and electrochemical techniques are combined to elucidate the effect of Cc and Cr implantation in the formation and evolution of passive layers generated by potentiodyinamic cycling on AISI 304L steel in alkaline medium. Cerium implantation promotes the formation of a thinner and more protective film on the steel. This fact, noticed in X-ray photoelectron spectroscopy (XPS) analysis, is reflected in the voltammograms by an important decrease of the magnetite formation and Cr3+/Cr6+ oxidation peak and, in the electrochemical impedance spectroscopy (EIS) diagrams, as the disappearance of one time constant. Chromium implantation contributes also to the generation of a thinner film, but more defective than in the case of cerium implantation. These differences are demonstrated in both electrochemical and surface analytical techniques. In the voltammetric curves, the diminution of the iron oxides signal is less notorious and an important increasing in the Cr3+/Cr6+ oxidation peak is registered. The EIS results show the persistence of the same number of time constants detected in the unimplanted steel. (C) 2004 Elsevier Ltd. All rights reserved.