The flow and mixing in a 3D geometrically accurate representation of a twin sigma blade mixer is simulated using the finite element method (FEM) combined with the mesh superimposition technique as implemented by Polyflow (Fluent, Inc.) to calculate the velocity, velocity gradients, shear rates, and mixing index. The mixing conditions and material models are based on those used in the laser-Doppler anemornetry (LDA) experiments of Prakash and Kokini. The simulation results are analyzed to determine the effect of increasing shear thinning on the flow and mixing, and are also compared with the experimental results of Prakash and Kokini for the purpose of validation. The results show how the increasingly shear thinning behavior of the chosen fluids changes the flow and mixing patterns at two blade configurations in a way that coincides with the LDA results of Prakash and Kokini. (c) 2006 Wiley Periodicals, Inc.