The adsorption of some substituted ferrocene molecules (Fc-R) on indium-tin-oxide electrodes has been investigated by cyclic voltammetry in acetonitrile. Adsorption occurs with carboxyl-substituted (R = -COOH and -(CH2)(6)COOH) and to a lesser extent With amino-substituted (R = -CH2N(CH3)(2)) ferrocenes. Adsorption from the neutral (ferrocene) carboxyl-substituted molecule produces layers with a coverage of 1 x 10(-10) mol cm(-2) which increases to 4 x 10(-10) mol cm(-2) from the oxidized (ferrocenium) molecule in air-saturated solution. In the latter case, adsorption occurs on a thin layer of amorphous iron oxide produced by oxidative decomposition of the ferrocenium. Electrodes modified by amorphous iron oxide layers are able to give stable monolayers from the carboxyl-terminated molecules, particularly with R = -(CH2)(6)COOH due to self-assembly. The layer structures are discussed on the basis of the adsorbate structure and the electrochemical parameters.