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A model is proposed to explain the biphasic reduction of ferricytochrome c at alkaline pH assuming an equilibrium distribution between a reducible and non-reducible conformer. An analysis of this model is given in an appendix to this paper. Protein denaturants, increasing pH and temperature are found to disturb the conformer equilibrium in favour of the irreducible form. The thermodynamic parameters governing this equilibrium have been determined. Kinetic parameters defined in the model were measured under a variety of conditions. The kinetic and equilibrium data strongly suggests that only the reducible conformer possesses the 695 nm band. Possible origins of the 695 nm band are discussed. [ABSTRACT FROM AUTHOR]