Electrorheological (ER) fluids made of starch particles in silicone fluid were studied under different electric field strength, particle concentration, water content, and shear rate. The ER fluids were sheared under constant shear rates during at least 210 min and the shear stress was measured. According to the results, the shear stress increased with time until a maximum was reached, decreased a little, and then stabilized. Some samples did not show a point of maximum, but after increasing with time, they stabilized at a given shear stress. The influence of the shear rate on the shear stress depended on the time the sample was sheared, on the electric field strength, on concentration, and on water content. The results were analyzed in terms of changes of lamellar formations in the direction of shear. (C) 2000 The Society of Rheology. [S0148-6055(00)01105-6].44511391149