Dissolution of magnesium was studied using an electrochemical flow cell combined with online analytics. The method has high sensitivity and congruency between electrochemical polarization experiments and magnesium concentrations detected downstream via inductively coupled plasma - mass spectroscopy (ICP-MS). The method used allowed quantification of magnesium dissolution during anodic and cathodic polarization and also without external currents, i.e. determination of dissolution rate at open circuit, which is not accessible by electrochemical techniques. The relationship between the applied current, and dissolved magnesium measured is presented and discussed in the broader context of past and recent works studying magnesium corrosion. The development of a surface film during anodic dissolution is described on the basis of an inventory of currents measured and applied. (C) 2014 The Electrochemical Society. All rights reserved.