Nanometer-sized semiconductor particles are currently being intensively investigated in many fields of physics and chemistry-especially since the discovery of visible luminescence in porous silicon. This is one of the first papers to concentrate on the synthesis of IV-IV nanoparticles. A purely wet-chemical room-temperature synthesis is described that leads to stable nanometer colloidal germanium particles after laser illumination. The size of the crystallites can be controlled by adjusting the illumination conditions. The preparation technique detailed here is not restricted to germanium but can also be applied to other IV-IV semiconductor particles.