A study was carried out to analyse the behaviour of internal flows in a closed grinding circuit. The study was performed through mathematical modelling, using the Cumulative Based Kinetic model and obtaining the necessary parameters at laboratory scale with various minerals. Particle size variations in all flows of the circuit were analysed with the aim of comparing the time it takes to reach a steady state. Results show in all cases that product flow reaches a steady state before the whole circuit does, mainly because the recirculation flow reaches a steady state with slower pace. More research at lab and industrial scale is being planned to try to corroborate this result. (C) 2010 Elsevier Ltd. All rights reserved.