Abstract: An electrostatic precipitator for operation at elevated pressures and temperatures comprises an inclined duct, usually of circular cross section, having the collector electrodes extending parallel to the axis of the duct and thus also inclined to the horizontal whereby the collected material can flow downwardly by gravity. The corona discharge electrodes, however, extend between frames spanned across the flow cross section and lying substantially in vertical planes, being tensioned by weights, advantageously via eccentric means such as levers.