Interfacial reactions in Ti-6Al-4V/SiC Sigma fibres (coated with carbon and TiB2) were studied at different temperatures (600, 700 and 1000 degrees C). Interface microstructure was investigated by scanning electron microscopy and Auger electron spectroscopy. A simulation of the chemical phenomena occurring at the interfaces was carried out using powders of pure titanium, carbon and TiB2; the reaction products were identified by X-ray diffraction. The double coating of Sigma fibres is effective in delaying detrimental reactions with the matrix. At the interfaces matrix/TiB2 and TIB2/C, the TiB and TiCx, phases form, respectively. The protective coating of fibres shows a lifetime greater than 1000 and 750 h at 600 and 700 degrees C, respectively.