The structural and electron-transfer properties of cytochrome c (Cyt c) Langmuir-Blodgett (LB) films have been studied on graphite electrode with tapping mode atomic force microscopy and cyclic voltammetry (CV). Cyt c in the LB films forms an ordered monolayer in which the individual proteins pack into a quasi-hexagonal structure. The monolayer undergoes a reversible electron-transfer reaction in phosphate buffer. The interactions of Cyt c with cardiolipin (CL) and phosphatidylcholine (PC) LB films have been studied. The LB films of CL and PC are both ordered on graphite, but their interactions with Cyt c are quite different. On a CL monolayer, Cyt c adsorbs spontaneously and the adsorbed protein preserves the electron-transfer reaction. However, on a PC monolayer, Cyt c does not adsorb.