The electron transfer reactions between a lipid-modified pyrolytic graphite (PG) electrode and four c-type cytochromes (monoheme cytochrome c and cytochrome c553 from Desulfovibrio vulgaris Hildenborough, tetraheme cytochromes c3 from D. vulgaris Hildenborough and D. desulfuricans Norway) have been studied by cyclic and square-wave voltammetry. No signal was detected at the PG electrode simply coated with a mixed layer of phosphatidylcholine (PC) and cholesterol (CH). The peaks corresponding to the reduction-reoxidation of cytochrome C553 were restored by doping the lipid layer with laurate anions (LA). In the case of cytochrome c, a rapid electron transfer reaction has been observed at the (PC-CH + LA)-modified PG electrode, accompanied by the progressive incorporation of protein molecules. By studying the effect of pH on the cv peak heights, it has been shown that the profiles for the four cytochromes depend on the protonation of the laurate anions and the protonation-deprotonation of protein species. The results support the electrostatic nature of the interactions between the cytochrome and the lipid layer but other factors (eg hydrophobic effects) are not excluded.