A detailed experimental study of the synthesis of transition metal nitrides via combustion reactions between gaseous nitrogen and the respective metal powders at elevated pressures is presented. Two representative combustion reactions were studied: between tantalum and nitrogen, which proceeds without the formation of any liquid phase, and between titanium and nitrogen, which is accompanied by melling of the reactant titanium powder. The effects of nitrogen pressure, metal particle size, porosity of the metal sample and dilution of the solid phase on the combustion characteristics were studied and optimum conditions for the synthesis of the respective nitrides were determined. Values of the apparent activation energies for the two reactions were extracted, based on combustion characteristics measurements.