Orthogonal superposition (OSP) rheology is successfully used in this work to study an electrorheological (ER) fluid composed of a starch/ silicone oil suspension. Interactions between hydrodynamic and polarization forces and other ER effects, such as the typical two-step yield stress observed when ER fluids are subjected to variable shear rates with simultaneous application of an electrical field, were evaluated. In order to conveniently investigate these effects, a specially designed geometry was mounted on a strain controlled rheometer. The OSP tests basically consisted of a continuous rotation and a simultaneous oscillation along the rotation axis (orthogonal to the rotation plane). On the other hand, by combining electro and OSP it is possible to evaluate how the electric potential influences the typical two-step yield stress of ER fluids in continuous rotation while the viscoelastic properties are simultaneously studied by OSP. Obtaining reliable storage and loss moduli in the axial direction while applying a rotational shear rate and an electric field allows to find out which part of the two-step yield corresponds to the elastic or viscous components. It is also observed that the moduli crossover varies linearly with the applied shear rate and there is a linear relation of the moduli crossover with the electric potential at which the crossover is observed. (C) 2016 The Society of Rheology.