Potential automotive applications of electrorheological (ER) fluids have stimulated renewed interest in their development. The inherent simplicity of a suspension of particles in a fluid that responds to an applied electric field with a two- or three-order-of-magnitude increase in viscosity is clearly attractive. However, there are some important parameters that are not well delineated. Among them is the ER-fluid response time, which needs to approach the millisecond range for effective device operation. We report results from recent measurements of response times for glass spheres suspended in silicone oil.