Summary: Electro-rheological and magneto-rheological fluids react to electric and magnetic fields respectively undergoing changes in their mechanical characteristics, viscosity and stiffness in particular. Their macroscopic behaviour is represented by the Bingham plastic model. In the last decade there has been an increasing attention toward the employment of ER and MR fluids in active bearings and active squeeze film dampers in rotordynamics. In the literature some applications of ER fluids in rotor squeeze film dampers can be found. However, nothing is reported on similar test rigs set up for MR dampers. After a review of the theoretical and experimental work reported in the literature, a feasibility study of an ER squeeze film damper and an MR one is presented and the two solutions compared.