The interaction of PAN-based T800H type carbon fibres, which had been coated with (i) pyrocarbon and (ii) pyrocarbon + SiC protective layers, was studied by means of SEM, energy-dispersive X-ray analysis and Auger electron spectroscopy. The interaction occurred during the pressure infiltration process at temperatures from 898 to 908 K and at contact times of 4-30 s. As detected by AES measurements, both Mg and Li penetrated throughout the carbon fibres, and Li2C2 was formed without remarkable reaction zone occurrence, which led to carbon fibre degradation. The pyrocarbon layer (about 50 nm thick) demonstrated a good protective efficiency and the corresponding metal-matrix composite exhibited satisfying strength characteristics; nevertheless, the influence of processing variables (temperature, time) was obvious. On the other hand, the double-coated pyrocarbon + SiC carbon fibres were strongly affected by Li2C2 formation.