The effect of replacing CaO by BaO on the glass transition temperature and on devitrification behaviour in a series of glasses in the calcium tetragermanate-barium tetragermanate composition range has been studied by differential thermal analysis (DTA), X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectra. A similar GeO4/GeO6 molar ratio was found in all the glasses of the series. The progressive replacement of CaO by BaO caused a decrease in the glass transition temperature. All the glasses studied exhibited internal crystal nucleation. The crystallizing phases were identified as CaGe4O9 and BaGe4O9. No solid solutions occurred in the glass containing both CaO and BaO. The effect of the specific surface of the glass samples on devitrification processes has also been studied.