Hybrid bilayer membranes (HBM) that consist of two different layers (a self-assembled monolayer of alkanethiols on a gold Electrode and a second layer of phospholipids) dramatically attenuate the heterogeneous electron transfer between soluble redox couples and the gold electrode. Alternating current voltammetry indicates the presence of a low density of defects in the HEM through which the redox couples can reach the electrode. Adsorption of a pore-forming cationic peptide, melittin, into the HEM increases the HBM capacitance, accelerates the faradic reaction for the negatively charged redox couple Fe(CN)(6)(3-), decelerates the faradic reaction for the positively charged redox couple Ru(NH3)(6)(3+), and has little effect on the faradic reaction of the neutral hydroxymethylferrocene. These results are discussed in terms of several possible mechanisms, including pore-forming processes and electrostatic effects.