0.8[xB(2)O(3)-(1 - x)SiO2]-0.2K(2)O (with 0 <= x <= 1) glasses were synthesized by melt quenching techniques. DSC curves of the glasses exhibit only one glass transition. Calorimetric measurements of heats of dissolution in lead borate at 973 K indicated small negative enthalpies of mixing. Consequently phase separation was not observed over the whole composition range. The results are in good agreement with the structural data available in the literature. (C) 2006 Published by Elsevier B.V.