We report the first study of interfacial reactions of a metal with Si1-x-yGexCy epitaxially grown on Si. The Ti/Si1-x-yGexCy/Si (0<y<1.7%) contact system was studied after isochronal heat treatments from 500 to 800°C. The results for Ti/Si1-xGex phase formation agree with recent published works. However, C incorporation in the epilayer causes a dramatic decrease in strain relaxation during the Ti reaction with the epilayer, a delay in the appearance of the C54 phase, a decreased Ge concentration in the silicide-germanide phases, and carbon accumulation (probably in the form of TiC) at the silicide-germanide/epilayer interface. Also, at high annealing temperatures, a roughing of the silicide-germanide/epilayer interface was detected for the C-containing samples. A possible explanation for the reduced strain relaxation is based on mobility of dislocations.