The field-activated combustion synthesis of the composites Ti5Si3 - x Nb (0 less than or equal to x less than or equal to 0.35) and Ti5Si3 - y ZrO2 (0 less than or equal to y less than or equal to 0.3) has been investigated. Composites with x greater than or equal to 0.35 and y greater than or equal to 0.2 can only be synthesized in the presence of an electric field. Although in the absence of a field the systems with x = 0.35, y = 0.2 and y = 0.3 can sustain a non-steady combustion wave, the reaction is not complete. An unstable wave propagates to the middle of the sample and then becomes extinguished. The wave velocity of the Ti5Si3-Nb and Ti5Si3-ZrO2 composites increased slightly with the application of a field.