A hydrophilic, macroporous filtration membrane in the form of a flat membrane based on a film-forming hydrophobic first polymer from the group of aromatic sulfone polymers, and a hydrophilic second polymer, wherein the membrane consists of a first and a second surface, and a supporting layer extending between the surfaces and having a three-dimensional sponge-like network structure, - wherein the supporting layer has a first cover layer on the side thereof facing the first surface and a second cover layer on the side thereof facing the second surface, which cover layers are formed integrally with the supporting layer, and - wherein the first and second surfaces have approximately oval or circular openings which penetrate the first and second cover layers, respectively, and are connected to the supporting layer, wherein the average diameter of the openings in the second surface is 0.5 to 1.5 times the size of the average diameter of the openings in the first surface and on condition that the average diameter of the openings in the first surface and the average diameter of the openings in the second surface differ by less than a factor of 2, - wherein the three-dimensional network structure of the supporting layer is made up of thick branches and a pore system with continuous pores, and at least 70% of the branches have a diameter at the thinnest point thereof, determined using scanning electron micrographs of cross-sections of the membranes at a magnification of at least 1000, of at least 0.5 μm, wherein the three-dimensional network structure does not contain any cavern-like pores, also referred to as finger pores; - wherein the pores in the supporting layer are larger than the openings in the surfaces; - wherein the filtration membrane has a thickness in the range between 50 and 150 μm; and - the average diameter of the openings in the second surface, determined using scanning electron micrographs, is in the range from 2 to 20 μm. - wherein the supporting layer has a first cover layer on the side thereof facing the first surface and a second cover layer on the side thereof facing the second surface, which cover layers are formed integrally with the supporting layer, and - wherein the first and second surfaces have approximately oval or circular openings which penetrate the first and second cover layers, respectively, and are connected to the supporting layer, wherein the average diameter of the openings in the second surface is 0.5 to 1.5 times the size of the average diameter of the openings in the first surface and on condition that the average diameter of the openings in the first surface and the average diameter of the openings in the second surface differ by less than a factor of 2, - wherein the three-dimensional network structure of the supporting layer is made up of thick branches and a pore system with continuous pores, and at least 70% of the branches have a diameter at the thinnest point thereof, determined using scanning electron micrographs of cross-sections of the membranes at a magnification of at least 1000, of at least 0.5 μm, wherein the three-dimensional network structure does not contain any cavern-like pores, also referred to as finger pores; - wherein the pores in the supporting layer are larger than the openings in the surfaces; - wherein the filtration membrane has a thickness in the range between 50 and 150 μm; and - the average diameter of the openings in the second surface, determined using scanning electron micrographs, is in the range from 2 to 20 μm.