Cytochrome c oxidase (CcO) catalyzes the four-electron reduction of oxygen to water, the one-electron reductant Cytochrome c (Cytc) being the source of electrons. Recently we reported a functional model of CcO that electrochemically catalyzes the four-electron reduction of O-2 to H2O (Collman et al. Science 2007, 315, 1565). The current paper shows that the same functional CcO model catalyzes the four-electron reduction of O-2 using the actual biological reductant Cytc in a homogeneous sotution. Both single and steady-state turnover kinetics studies indicate that O-2 binding is rate-determining and that O-O bond cleavage and electron transfer from reduced Cytc to the oxidized model complex are relatively fast.