The structures of two series of lanthanum gallogermanate glasses are investigated by the Fourier transform infrared (FT-IR) spectroscopy. These glasses show excellent infrared transparency up to the mid-IR (6-7 mum) region. The structural roles of lanthanum, gallium and germanium ions are discussed. Evidence of the existence of both tetrahedral (four-fold coordination) and octahedral (six-fold coordination) of Ga and Ge has been found in the glass networks of these glasses. (C) 2004 Published by Elsevier B.V.