Liquid displacement of model and industrial fluids in pipes was successfully investigated using the in-line rheometer concept based on the combination of Ultrasound Doppler Velocity Profiling (UVP) and the pressure difference (PD) technique. The velocity profile development, related mixing zone and real-time changes in rheology were monitored when one fluid was displaced by another with different rheological properties. Four sets of model systems, all well described by the power law model and relevant for the food industry, were used to adequately cover different classes of fluids. In addition, two sets of industrially produced foods with similar flow characteristics were used to test the industrial applicability and limitations of the UVP-PD methodology developed. The results demonstrate that the in-line UVP-PD rhemeter concept is an attractive multi-point method for real-time process monitoring and control of non-Newtonian fluids. (C) 2010 Elsevier Ltd. All rights reserved.