This study investigates the application of the Constant Temperature Anemometry (CTA) technique to determine the flow distribution among hollow fibre bundles in a submerged membrane system. Membrane filtration was performed at constant permeate flux with five submerged hollow fibre membrane mini-bundles, representing regions of a submerged module, operating in parallel through a common suction pump. Five CTA sensors were located in a matrix above the outlets of the bundles so that the individual contributions of each bundle region to the net permeate flow could be monitored. This allowed measurement of the system response to simulated localised fouling or blocking, aeration failure and restoration of aeration. The CTA sensors were able to monitor the permeate flow distribution among the fibre bundles when mal-distribution of flow occurred in the system. Satisfactory performance of the CTA sensors was verified by comparing the amount of cake deposited on the membrane surface of the fibre bundles with the local flux behaviour. The results demonstrated the potential of using the CIA approach to characterise the cross-sectional fouling or blocking variation in a submerged hollow fibre membrane system. It is evident that this approach could be applied in other module configurations. Technical challenges to this CTA application are discussed. (C) 2009 Elsevier B.V. All rights reserved.