Metal wires and metal-oxide-metal junctions were fabricated by anodic oxidation with the conducting tip of an atomic force microscope (AFM). The width of the wires and resistance of the junctions were controlled by real-time, in situ measurement of the device resistance during fabrication. Because the properties of nanometer-scale devices are very sensitive to size variations, such measurements provide a more accurate method of controlling device properties than by controlling geometry alone. In this way, structures with critical dimensions of less than IO nanometers were fabricated with precisely tailored electrical properties.