The significance of keeping under control the rheological behaviour of the suspensions used in dense medium separation is highlighted. Some workable enhancements of the complex plant circuitry leading to the possibility to modulate the viscosity or operating media are proposed. With a stepwise procedure, the complexity or establishing a framework for the quantitative description or the medium viscosity is described. Adopting a simplified approach which considers the solid phase or the medium as made up by a binary blend (magnetite + contaminant), separate expressions have been defined for describing the dependence of the relative viscosity on the volume fraction of the disperse phase, its composition and the flow conditions (shear rate). Introducing some corrective parameters for taking account of more complex composition characteristics of the solid phase and combining the above mentioned expressions a final rheological model suitable for practical use is obtained. This model allows predicting the relative viscosity of dense media as a function of the major medium composition variables and of the operating Sow conditions.