The open circuit potential (OCP) of CoCrMo alloy before, during, and after mechanical disruption of the passive film is recorded in inorganic buffer solutions in the pH range 3.0-10.0. The OCP values in the active state show a different dependence on solution pH in acidic and alkaline pH. The results obtained from cathodic polarization experiments and the information suggested by the Pourbaix diagrams of cobalt and chromium together with mixed potential theory are used to interpret the electrochemical behavior of CoCrMo alloy in the active state. At acidic pH cobalt and chromium oxidize giving the bivalent aqueous ions Co(II) and Cr(II) as primary oxidation products, while the cathodic partial reaction is the hydrogen evolution reaction. At alkaline pH cobalt and chromium originate the oxide species CoO and CrO while the oxygen electronation reaction supplies the oxidation current. The repassivation rate is estimated by monitoring the OCP increase 30 s after the passive film is mechanically destroyed. The percentage increase in the OCP is referred to the steady-state open-circuit values 1 h after mechanical disruption of the oxide film. The repassivation rate decreases with increasing pH because the coprecipitation of unstable cobalt oxide species hinders the formation of the chromium oxide passive film. (C) 2003 The Electrochemical Society.