The electrochemical behavior of horse cytochrome c attached covalently in various orientations to the surface of a glassy carbon (GC) electrode has been studied. The electric field of the electric double layer was used to orient the molecules at electrode. The oriented protein molecules were fixed using a carbodiimide preparation. Voltammetric analysis of cytochrome c attached under various potentials applied to the GC electrode (or in various electrical fields) showed sharp changes in the peak currents in the range of potentials close to the zero charge point. A negative charge on the electrode promoted the attachment of cytochrome in an orientation favorable for electron transfer. This is consistent with the structure and dipole direction in the protein molecule. A positive charge on the electrode resulted in an electrochemically inactive orientation. On the basis of experimental evidence it was concluded that the poor electrochemistry of cytochrome c attached at positive potentials is caused only by unsuitable orientations. The degree of coverage of the electrode surface by attached cytochrome c was determined using laccase as an enzyme label. The potential ranges in which cytochrome c is effectively attached and in which it remains in its native state were determined. Peak potential separation was found to be independent of the conditions of cytochrome c attachment. A possible explanation for this unexpected result is proposed.