Because of kinetic limitations, self-sustaining combustion synthesis reactions cannot be initiated in dense powder compacts. In compacts of Mo + 2Si, self-propagating waves can be initiated in samples with less than 78% relative density. At this and higher densities, no waves could be initiated without field-activation. In the presence of an electric field (at values of 7 and 13 V⅐cm −1 ), reactant compacts with densities up to 95% could sustain a combustion wave to produce MoSi 2 . In the absence of a field (for lowerdensity samples) the wave propagated in a non-steady-state (pulsating) mode, while under the influence of a field the wave propagated in a steady-state mode. The dependences of wave velocity and combustion temperature on the relative density of the reactants were qualitatively similar, showing maxima at a relative density of about 65%. These observations are explained in terms of the contribution of a liquid phase in the MoSi 2 -Mo 5 Si 3 binary to the synthesis kinetics. Although not detected by X-ray diffraction analysis, small amounts of Mo 5 Si 3 were discerned at the grain boundaries of the MoSi 2 product. The particle size of the silicide synthesized from 95% dense reactants was significantly smaller than those synthesized from reactants with lower densities, but the reason for this observation is not well understood at this time.