The growth of TiO2 nanotubular layers on sputter-deposited Ti thin films was investigated in glycerol/NH4F electrolytes. The growth morphology, the kinetics of tube growth and particularly the chemical etching rate of the tubes strongly depend on the water concentration. The present work shows that in an optimized electrolyte consisting of high-purity glycerol with small additions of NH4F, regular, smooth-walled TiO2 nanotubes can be grown with high current efficiencies. Therefore, this approach allows the full and highly defined conversion of sputter-deposited Ti substrates into TiO2 nanotube layers at room temperature. (C) 2008 The Electrochemical Society.