Sterically stabilized polypyrrole latex particles attached to Au substrates were observed to adsorb imidazole and histidine from aqueous solutions by ellipsometry. In initial studies the imidazole ring adsorption was mainly irreversible, but after electrochemical reduction-oxidation cycling of the particles in HCl solution only reversible adsorption of the heterocyclic compounds was observed. Adsorption experiments on control surfaces containing the different components of the latex particles identified iron species incorporated during synthesis as the probable irreversible adsorption sites. The reversible adsorption sites were possibly due to the acidic properties of the polypyrrole core in the particles.