A two-stage electrostatic filter includes an ionization section which is arranged in an upstream part of a throughflow passage (28) and includes a wire-like corona electrode (31) which is disposed in an ionization chamber (29) and connected to one pole of an electric high voltage source (16). The filter further includes a target electrode (21; 37) which is spaced from the corona electrode (31) and connected to another pole of the high voltage source. A capacitor separator (30) is located in a downstream part of the throughflow passage (28) and includes a first and a second group of electrode elements (32, 33) which are placed side-by-side in spaced-apart relationship. The electrode elements (32) of the first group are placed alternately with the electrode elements (33) of the second group and are adapted to lie on a potential which is different from the potential on which the electrode elements (33) of the second group lie. The ionization chamber (29) has a target electrode surface (37; 21) which is disposed both upstream and downstream of the corona electrode (31). When measured perpendicularly to the upstream-downstream direction of the throughflow passage (28) and to the longitudinal axis of the corona electrode, the distance of the corona electrode (31) from the target electrode surface is at least four times the distance between neighbouring electrode elements (32, 33). The capacitor separator (30) and the ionization chamber (29) form a disposable unit made of a non-metallic material, preferably a cellulose fibre material.