Tomographic signal processing has been added to a conventional electromagnetic flowmeter. The result is a new method for measuring rheological parameters of viscous, non-Newtonian fluids. Tile practical realization requires only minor changes lu existing instruments. Hence their main advantages are maintained, such as non-invasive. in-line measurement without pressure drop. The basic idea is to generate two different magnetic fields with the flowmeter by switching thr current direction in one of the magnetic coils. The flowmeter measures two signals depending on the flow profile. Using simple parametric models for both the flow profile and the rheology. the How profile can be calculated from the flowmeter signals, and from the flow profile the rheological behaviour is determined. The theory and experimental results with a slightly modified industrial flowmeter are presented.