A large-scale electrical tomography system has been designed and set-up at UMIST to study imperfect mixing and improve the design of stirred vessels and their impeller configuration at plant-scale. The sensing system was constructed with 8-planes of sensing rings, each containing 16-electrodes and installed into a 2.7 m(3) polypropylene vessel fitted with a standard Rushton turbine. Images were reconstructed using the sensitivity theorem algorithms. Some illustrative results for pseudo-stationary gas-liquid mixing and unsteady semi-batch mixing of miscible fluids are reported. Issues related to qualitative and quantitative reconstruction in 2-D and 3-D are discussed.