A novel method is demonstrated to tailor the electronic structure of high-Z surface alloys showing a giant Rashba splitting by means of electron doping. This aims for new model systems to study unconvential spin topologies and for possible applications in the field of spintronics. We give new insights into the origin of the enhanced Rashba effect in the two specific alloys Bi/Cu(111) and Bi/Ag(111) employing angle-resolved photoelectron spectroscopy and first-principles calculations. Copyright (C) EPLA, 2009