We have detected stimulated far-infrared emission from copper-doped germanium single crystals. By varying the magnetic field between 1 and 2.3 T, we have achieved emission in the range of 70–120cm−1.Laser action was observed for crystals with a copper acceptor concentration as high as1.5×1015cm−3,a doping level that is considerably higher than that of any single or double acceptor doped Ge laser. Stimulated emission from Ge crystals with such a high Cu concentration is possible because only a small fraction of the copper acceptors is ionized during operation. ©1997 American Institute of Physics.