The electrochemical properties of cytochrome c (cyt c) immobilized on multilayer nanozeolite-modified electrodes have been examined in aqueous and nonaqueous solutions. Layers of Linde type-L zeolites were assembled on indium tin oxide (ITO) glass electrodes followed by the adsorption of cyt c, primarily via electrostatic interactions, onto modified ITO electrodes. The heme protein displayed a quasi-reversible response in aqueous solution with a redox potential of +324 mV (vs NHE), and the surface coverage (Gamma*) increased linearly for the first four layers and then gave a nearly constant value of 200 pmol cm(-2). On immersion of the modified electrodes in 95% (v/v) nonaqueous solutions, the redox potential decreased significantly, a decrease that originated from changes in both the enthalpy and entropy of reduction. On reimmersion of the modified electrode in buffer, the faradic response immediately returned to its original value. These results demonstrate that nanozeolites are potential stable supports for redox proteins and enzymes.