The formation and stability of the products of Ti and Co reacting with Si1-xGex substrates were investigated. For the Ti/SiGe system, when a C54 Ti(Si1-yGey)(2) layer forms, the Ge index y is initially the same as the Ge index of the Si1-xGex substrate (i.e. y=x). Thereafter Si1-xGex from the substrate continues to diffuse into the C54 layer via lattice and grain-boundary diffusion : Some of the Si which diffuses into the C54 lattice replaces Ge in the lattice, and the C54 Ti(Si1-yGey)(2) becomes silicon enriched (i.e. yx) islands were observed. It was found that for Co/Si1-xGex the reacted layer consisted of CoSi2 and Si1-zGez after high-temperature annealing (approximate to 700 degrees C). We propose that these processes are driven by a reduction in the crystal energy of the C54 Ti(Si1-yGey)(2) phase in the Ti/SiGe system and the Co(Si1-yGey) phase in the Co/SiGe system which accompanies the replacement of Ge with Si.