The relative energies of chemisorption of molecules on a clean lead surface have been computed with an extended Hückel molecular orbital method. The calculations were carried out with several organic molecules in order to investigate the formation of monomolecular layers and their possible use as thin (10–20 Å) insulating Josephson tunneling barriers. Calculating the adsorption energy at various locations on the Pb surface yields a measure of the surface coverage and the most suitable organics for forming the monolayer. Nonoxidative adsorbates are found not to chemisorb on Pb while those which are oxidative do bond. The bonding energy of the acetoxy radical is found to be 4 eV and the ethyl radical energy is 0.6 eV.