Electromigration test structures consisting of 0.1-0.5-mu m-wide and 0.25-mu m-thick Al(4%Cu) wires and W contacts have been fabricated on 70-nm-thick Si3N4 membranes using electron-beam lithography and reactive-ion etching. Observation of grain structure evolution with electromigration in these wires by transmission electron microscopy is reported. It is shown that dissolution of Al2Cu grains is accompanied by the growth in neighboring Al grains.