The preparation of self-assembled alkanethiol monolayers and alkanethiol \ phospholipid bilayers on a home-made hanging mercury drop electrode is described. Two different experimental procedures are used to prepare alkanethiol monolayers on mercury. Once a stable thiol monolayer is obtained on the mercury electrode, formation of the bilayer is simple and highly reproducible. The bilayers consist of a thiol monolayer anchored to mercury via the sulfur atom, with a second phospholipid monolayer on top of it. Monolayers and bilayers are characterized electrochemically by measuring capacitance and resistance. Both thiol-coated and thiol I lipid-coated mercury electrodes present a compact and well-ordered structure, absence of defects and high reproducibility. The permeability of these films to compounds with different degrees of lipophilicity is examined. The results point to a high impermeability of self-assembled alkanethiol monolayers and mixed alkanethiol I phospholipid bilayers supported by mercury to lipophilic compounds.