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We have applied a magnetoresistive microscopy technique to the imaging of current densities and pinhole formation in magnetic tunnel junction devices. In this work, we demonstrate how the magnetic field distribution at the surface of the device can be used to understand the flow of current within the junction itself. By imaging the current-induced fields before and after pinhole formation in several different junctions, we find that many junctions exhibit an unexpectedly complicated current distribution after high-voltage-induced breakdown. Further, we have seen that pinhole locations can be correlated with current inhomogeneities observed before junction breakdown. Finally, we present the results of finite-element simulations which are in good agreement with experimental results. © 2004 American Institute of Physics.