A simple method is proposed for testing the reactivity of elemental iron materials (Fe-0 materials) using methylene blue (MB) as reagent. The method is based on the oxidative reactivity of Fe-II for reductive dissolution of MnO2. Fe-II is produced in-situ by the oxidation of a Fe-0 material. The in-situ formed Fe-II reacted with MnO2 delaying the bulk precipitation of iron corrosion products and thus MB co-precipitation (MB discoloration). For a given MnO2, the extent of MB discoloration delay is a characteristic of individual Fe-0 materials under given experimental conditions. The MB discoloration method for testing the reactivity of Fe-0 materials is facile, cost-effective and does not involve any stringent reaction conditions. (C) 2009 Elsevier B.V. All rights reserved.