With increasing use of biomass in combustion processes, the reduction of the related NOx emissions which originate mainly from the fuel nitrogen becomes more and more important. Efficient primary measures for NOx reduction are staged combustion techniques. Air staging has been investigated earlier and has found its way into practice. Since fuel staging-has not been applied with nonpulverized biomass yet, the aim of the present work was to investigate the potential of fuel staging for NOx reduction in fixed bed systems. For this purpose, a prototype understoker furnace of 75 kW thermal input with two fuel beds in series was developed. Experiments were performed with wood chips (low nitrogen content) and UF-chipboards thigh nitrogen content) to investigate the influences of the main process parameters, i.e., stoichiometric ratio, temperatures, residence time, and fuel properties on the conversion of fuel nitrogen to N-species. The most important parameters were found to be the temperature and the stoichiometric ratio in the reburn zone. The potential of fuel staging was measured and,compared with air staging and unstaged combustion. The experiments show that low NOx emissions are already achievable with fuel staging at lower temperatures than with air staging, i.e., 900-1000 degreesC, and at a stoichiometric ratio of 0.85 in the reduction zone. The NOx reduction achieved under optimum conditions for UF-chipboard as main fuel was 78% which is higher than with air staging, where 72% NOx reduction was measured. For wood chips both measures attained about 66%. The nitrogen conversion during air and fuel staging has also been simulated using a furnace model based on ideal flow patterns as perfectly stirred reactors and plug flow reactors. A:detailed reaction mechanism including the nitrogen chemistry (GRI-Mech 2.11) was implemented. The trends found with this model are in good agreement with the experiments and they indicate that even higher NOx reduction may be reached with improved process design. The investigations show that fuel staging is a promising technology for NOx reduction also for fixed bed biomass furnaces.