Schlieren visualization and laser-anemometry experiments are presented which demonstrate that a two-dimensional positive corona discharge interacts with the flow of a wire–plate electrostatic precipitator to produce a non-turbulent secondary flow in a plane perpendicular to the discharge wires. Smoke-wire visualization and hot-wire anemometry experiments are then described which show that negative-corona-discharge non-uniformities are responsible for producing both secondary flow in a plane parallel to the discharge wire and also turbulence. The significance of these results to the performance of electrostatic precipitators is discussed.