We have succeeded in growing single crystals of the oxide spinels GeNi2O4 and GeCo2O4. Both materials have the pyrochlore lattice, and show anti ferromagnetic-like order. Thus, magnetic frustrations and relevant phenomena are strongly expected. To obtain single crystals of these materials, we employed a conventional floating-zone method. For the crystal growth of GeCo2O4, no severe difficulties were found. For GeNi2O4, it was necessary to avoid intense the evaporation of GeO2 due to the higher melting point of GeNi2O4 than that of GeCo2O4. Therefore, it was quite difficult to obtain single crystals of GeNi2O4 by the same procedure as GeCo2O4 We show the importance of the starting composition and crystal growth atmosphere for both spinels. (c) 2005 Elsevier B.V. All rights reserved.