During electrochemical micro machining (ECMM) metals are electrochemically dissolved at very high current densities up to 100 A/cm(2) in aqueous electrolytes like NaNO3 or NaCl. Different anode processes take place during the electrochemical machining (ECM) process of iron in NaNO3. Iron is dissolved as Fe2+ and Fe3+ and oxygen evolution appears. The different reaction products are analysed quantitatively and time resolved for pulses 10 ms less than or equal to t(pulse) less than or equal to 5000 ms under ECM conditions by a combination of our flow-through-microcell with an UV-vis-spectrometer and a pulse generator. The surface structure during pulsed ECM and the appearance of the machined surface is shown in dependence of the pulse length and the prepolarisation of the electrode. Crucial for the obtained results are the build-up and removal of the oxides. as well as the polishing film. The model for stationary ECM conditions is extended to a time resolved model. (C) 2004 Elsevier Ltd. All rights reserved.