The shear rate distribution in the model mixer, the Brabender Farinograph, is non-homogenous and varies with the relative positions of the sigma blades, which rotate at differential speeds. The non-invasive technique of Laser-Doppler Anemometry (LDA) was used to determine velocity and shear rate distributions in the mixer. A two-dimensional argon-ion Laser-Doppler Anemometer was used to obtain three-dimensional velocity measurements in the model mixer with optically clear model fluids (Corn syrup, CMC, and Carbopol-940 seeded with polystyrene DVB microspheres). Local velocity gradient data obtained using infinitesimal movements of the traverse were used to calculate the shear rate distribution in the model mixer. The shear rate was found to be a function of blade geometry, blade position, and location. Shear rate values ranged from 0 to 400 s(-1). Based on these data, a predictive equation for shear rate in the model mixer was developed. (C) 2000 Elsevier Science Ltd. All rights reserved.