The aim of this work is to identify a proper Computational Fluid Dynamics (CFD) simulation strategy for the calculation of mixing time in stirred tanks for fluids characterised by either Newtonian or non-Newtonian theological behaviour. Two different baffled tanks are considered, both stirred with multiple down-pumping 45 degrees pitched blade turbines (PBT): a small one for extensive, preliminary simulations conducted with water and aimed at determining a generic procedure suitable with low-viscosity, Newtonian liquids; and a bigger one for testing the results with moderately viscous liquids and non-Newtonian fluids. The influence on the predicted mixing time of the tracer injection position, turbulence modelling and numerical parameters is investigated. The results of the simulations are compared with original experimental data and good agreement is obtained in all cases, once the proper mathematical models, solution procedure and relevant parameters are established. (c) 2004 Elsevier Ltd. All rights reserved.