A selective electrodeposition method for the fabrication of extremely thin and long metallic and magnetic wires is introduced. Growth is done on the cleaved edge of a semiconductor multilayer structure incorporating a 4-nm-wide modulation doped quantum well. This conducting quantum well is connected to the negative current contact during electrodeposition. Since electrodeposition requires the neutralization of positive metal ions from the solution, deposition takes place selectively onto the edge of the quantum well, leading to the fabrication of extremely thin magnetic metal wires, which should be useful for the investigation of the limits of magnetic storage. ©1997 American Institute of Physics.