Dense hot-pressed beta-Si3N4 blocks were joined using both SiO2 and SiO2-Y2O3 powder slurries as bonding interlayers. The assembled specimens (Si3N4/interlayer/Si3N4) were heated in a flowing N-2 atmosphere in the temperature range of 1500degrees-1650degreesC. The joining interlayer was clearly distinguished from the Si3N4 bulk. The microstructure and the reaction products found in the bonding interlayer were very different in both compositions. Reactions occurring between the Si3N4 and the ceramic joining compositions have been explained based on existing diagrams of the YN-Si3N4-Y2O3-SiO2 system.