30 vol% of TiB2, TiCN, TiN or TiC was added to a sialon matrix with an X-phase sialon (Si12Al18O39N8) and an Al2O3-Si3N4 (77/23 wt%) starting powder composition and hot pressed at 1650degreesC in vacuum. The microstructures of the obtained composites were characterised by means of X-ray diffraction and electron microscopy, and the mechanical properties; E-modulus, hardness, bending strength and fracture toughness were measured and evaluated. Fully dense composites with an X-phase sialon or a polyphase Al2O3-beta-sialon-X-sialon matrix with 30 vol% of TiB2, TiN and TiCN were obtained. TiC, added as a dispersed phase, however reacts with the nitrogen from the Si3N4 during liquid phase sintering, with the formation of TiC1-xNx, SiC and a changed sialon matrix composition. In the case of the X-phase sialon starting composition, a mullite matrix is obtained after sintering. The microstructural observations with respect to the sialon-TiC composites are found to be in agreement with the thermodynamic calculations. (C) 2004 Kluwer Academic Publishers.