The inhibiting action of six o-substituted anilines against the corrosion of iron (99.9999%) in solutions of sulphuric acid has been studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). At inhibitor concentration range (10(-3) to 10(-2) M) in 0.5 M acid, the efficiency of the inhibitors increases in the order o-toluidine < 2-chloroaniline < 2-ethylaniline < 2-fluoroaniline < o-aminoanisole < 2-amiophenetole. Comparable results were obtained by the different electrochemical methods used. Adsorption of these compounds on the iron surface was found to obey a Langmuir adsorption isotherm. An equivalent circuit is suggested based on analysis of EIS data. (C) 2003 Elsevier B.V. All rights reserved.