Diamond reinforced metals with a diamond content of 55-60 vol.% were made by gas driven liquid metal infiltration. They were characterized with regard to their stiffness, strength and fracture toughness as a function of diamond particle size and matrix alloy by means of tensile and Chevron notch tests, respectively. The choice of the metal matrix, i.e. pure Al, Al-Cu, Cu-B and Ag-Si alloys was made in view of their application in thermal management where high thermal conductivity is important. For undamaged material Young's moduli, measured in unloading-reloading cycles necessary to measure static Young's modulus, of 250 GPa for Al-based and 300 GPa for Ag-based composites were obtained. The copper-based composites exhibited much lower values indicating that the small deformation necessary to measure Young's modulus induced already considerable damage. Strain to fracture of the composites was found to be a few tenth of a percent. An ultimate tensile strength of approximately 300 MPa was reached for the silver-based composites compared with roughly 150 MPa for the Al-based and below 50 MPa for the Cu-based composites. The size of the diamond particles had little influence on stiffness and strength of the composites but fracture toughness increased with increasing particle size. The differences in the mechanical behaviour of the configurations investigated can be rationalized by observations made during fractographic investigations by scanning electron microscopy. Additionally, the damage evolution in the composites was observed by the repeated determination of the specimen's stiffness during the tensile tests.