Methylene blue dye (MB) was investigated as a corrosion inhibitor for mild steel in 2 M sulphuric acid solution using gravimetric and thermometric techniques. The inhibition efficiency of MB increased with concentration and synergistically increased in the presence of the halide additives, namely KCl, KBr and KI. The trend of inhibition efficiency with temperature suggests that inhibitor molecules are physically adsorbed on the corroding metal surface at lower concentration (0.01-0.5 mM), and chemically adsorbed at higher concentration (1.0-5.0 mM). These results were further corroborated by kinetic and activation parameters for corrosion and adsorption processes evaluated from experimental data at the temperatures studied. MB was found to obey Langmuir and Frumkin adsorption isotherms in the concentration range investigated. (C) 2004 Elsevier B.V. All rights reserved.