Previous works demonstrate that biomass is a valid reburn fuel, displaying NOx reductions close to those obtained in natural gas reburning. However, available information on biomass reburning basically refers to parametric studies based on exhaust emissions, lacking a thorough description of the process. The present work is an attempt to provide a detailed experimental characterisation of biomass reburning, including parametric studies in propane and pulverised coal flames, as well as in-furnace spatial distributions of the relevant variables. The tests were performed in a semi-industrial-scale furnace. Both natural gas and sawdust were used as reburn fuels for a range of residence times (0.41-1.44 s) and stoichiometries (0.85-1.05) in the reburn zone. NOx and unburnt (CO and UHC) emissions were measured in all the tests. A detailed characterisation of the local temperatures and concentrations of CO, UHC, NOx, HCN and NH3 inside the reducing zone was accomplished for some selected cases. (c) 2008 Elsevier Ltd. All rights reserved.