Membrane (carbon or gold) electrodes constructed from dialysis membranes varying in cutoff and charge are used to investigate the electrochemical behavior of c-type cytochromes, especially cytochrome c. It is shown from cyclic voltammetry experiments that cytochrome c exhibits direct electrochemical responses at negatively charged membrane (graphite-, glassy carbon-, mercury film glassy carbon-, and gold) electrodes. Different factors (pre-treatment of the membrane, effect of positively charged species, ionic strength, pH, effect of the entrapped layer thickness) have been examined. The electrochemical response of multiheme cytochromes c 3 at the membrane electrode is also investigated. It is demonstrated that the electrochemistry of cytochrome c at the membrane electrodes is essentially governed by favorable electrostatic interactions, and that other factors (especially adsorption and the presence of denatured forms) do not play a dominant role. A discussion on the electrochemistry of c-type cytochromes is given.