The electrochemical behavior of the electron transfer proteins (cytochromes b5, c and P-450) was studied by classical polarography and electrolysis with spectrophotometric monitoring. Electrons are evidently directly transferred from the electrode to oxidized cytochromes c and b5. Cytochrome P-450 is not reduced on the electrodes. The reduced inactivated form of cytochrome P-420 was detected at high potential values (-1,5 V).