Abstract: A return filter for hydraulic fluids comprises a filter head attachable to a container for fluid, a filter pot arranged on one side of the filter head, a cover releasably arranged on the other side of the filter head, a filter element arranged so as to extend continuously through the filter head and the filter pot, at least one inlet formed on the filter head for the returning fluid, an air port formed on the filter head, and a ventilation filter inserted into this port. Filter head, filter pot and filter cover consist of plastic; a hose nipple integral with the filter head is formed at the inlet for the returning fluid. The air port is surrounded by a housing which is integral with the filter head and is closable by a cover carrying the ventilation filter. The walls of the housing are provided with slots which are open towards the cover. On the one hand, these slots make provision for air to pass through and, on the other hand, they allow the cover to be releasably clipped into the housing.