Gas-solid systems are among a large class of systems in which self-propagating hightemperature synthesis (SHS) is observed. Powders of metals and non-metals burn in the atmosphere of gaseous reagent and the products of the reaction are solid. A variety of nitrides and different composites were synthesized by combustion of porous powder compacts in nitrogen atmosphere. The conversion, achieved during the combustion process, as well as the composition and structure of the products, significantly depends on the nitrogen pressure. Most of the published experimental results on this topic were obtained under nitrogen pressure of less 10 MPa and only few systems were investigated under higher pressures. In this work we present the results of the studies on the combustion process in the range of high nitrogen pressures of 40-400 MPa for two systems, such as Nb-N2 and B-C-N2. Dependences of combustion characteristics, phase composition and microstructure of the synthesized products on the nitrogen pressure were studied.