A new device has been constructed for measuring of rheological properties of rapidly sedimenting suspensions. It is a double-gap coaxial fixture attached to a driving unit of a commercial rheometer. The suspension is kept from sedimenting by circulation which influences the results and, therefore, should be stopped during measurement. The influence of the circulational axial flow on the measured viscosity was presented on examples of a contaminated and pure magnetite dense medium. It is due to the additional shearing caused by the axial flow and to the inertia of the entering fluid to which the rotation must be applied.