The rheological, dielectric and structural behavior of suspensions composed of silicon oil and asphaltene particles under DC electric fields are investigated experimentally. In the absence of an electric field, the suspensions show a near Newtonian behavior. When the electric field (E) is applied, the suspensions behave as Bingham plastics with a yield stress that varies as a power of the electric field. The increase in the viscosity of the suspensions (electrorheological phenomenon, ER) is more accentuated at low shear rates and depends on the electric field intensity. The resulting rheological behavior can be attributed to the formation of structures induced by the electric field, and they brake when the shear rate is increased. The relation between the structural arrangements of the suspension under an electric field and the rheological behavior is analyzed in this study. Results show that the ER response of asphaltene suspensions is not as large as that observed in conventional ER fluids, but nevertheless they throw light on the contribution of electrorheological mechanisms upon asphaltene particle aggregation observed in the transport of the crude oil in the petroleum industry. (C) 2004 Elsevier Ltd. All rights reserved.