The pyrolysis of pine sawdust has been carried out in a High-Temperature Fluid-Wall Reactor. This unit has been specially designed to withstand working temperatures of up to 2200° C. The biomass is fed to the top of the reactor after sieving to the appropriate size, at a rate of 1.0 to 1.8 kg/min. The feed falls and, at the same time is very quickly heated by radiation to the reaction temperature. The estimated heating rate is on the order of 106° C/s for reactant surfaces. The fluid-wall, produced by a nitrogen flow through the 30 cm diameter porous reactor core, prevents both reactants and products from reaching the reactor wall. The product distribution at the reactor exit has been determined for different operating conditions. The influence of reactor temperature, biomass feed rate, and biomass particle size on the product distribution and on the heating value of the exit gas has been investigated.