Scanning electrochemical microscopy (SECM) in surface generation/tip collection mode is investigated as an assessment tool for studying the corrosion behaviour of magnesium in simulated biological fluid. The technique provides a local map of hydrogen (H-2) evolution which alone can be used as a direct measure of corrosion. The H-2 generated during corrosion of magnesium is oxidized at the probe(i.e. a Pt ultra microelectrode); with the magnitude of the current generated due to oxidation being indicative of the intensity of H-2 evolution at a local scale on the magnesium surface. This methodwas calibrated using a cathodically polarized Pt disk to simulate H-2 evolution in a controlled condition on a homogeneous surface. Potential interference from dissolving Mg or high local pH was also investigated. The technique was implemented for studying H-2 evolution at the surface of AZ31 as a model Mg alloy. SECM results combined with SEM-EDX and profilometry data revealed that local domains of higher H-2 evolution on the surface of AZ31 are in close proximityof the observed pitting sites. (C) 2014 Elsevier Ltd. All rights reserved.