Summary form only given. In this paper, we present a new technique for fault isolation and failure analysis in integrated circuits, based on a scanning magnetoresistive imaging system. By detecting the stray magnetic fields at the surface of a chip using magnetic sensors with sub-micron spatial resolution, we are able to obtain a full map of in-plane current densities, resolving features smaller than 100 nm. We briefly discuss the capabilities and limitations of the technique and present results on a variety of frontside and backside samples.