3D Laser Doppler Anemometry (LDA) and flow visualisation were used to investigate the burner-burner interaction on an isothermal physical model of a front-wall fired furnace. Four different pitches arranged in a 3 X 3 array were tested. From the flow visualisation study it was observed that, as pitch decreased, interactions between burners became more evident. It was also observed that isothermal burner jets were fluctuating in their width arbitrarily, thus exhibiting time-dependent features. The LDA results clearly showed differences between flow velocity patterns occurring at different pitches and different configurations. It was found that both recirculation and jet penetration were more sensitive to the change of configuration for the smaller pitches. Equally, the sensitivity to the change in pitch was higher in the case of the chequered board configuration. The results presented here will be used to validate a Computational Fluid Dynamics combustion model, so that the effect of burner-burner interactions on NOx emissions can be accurately predicted. (C) 2003 Elsevier Ltd. All rights reserved.