A filtration container for concentration of macromolecules is insertable into a filtrate recovery tube (5) and has an upper portion (2), a central portion (3) axially adjoining the upper portion (2), and a lower portion (4) axially adjoining the central portion (3). The upper portion (3) forms a hollow-cylindrical sample container (7) with an inlet opening (9) on its upper end face (8). The downwardly tapering central portion (3) has a filtration chamber (11) with two mutually opposed main walls (12, 13) running down toward one another. At least one of the main walls (12, 13) has a filter window (16) for receiving a planar membrane filter (17). The lower portion (4) forms a retentate chamber (21) adjoining the lower edge (18) of the filter window (16) A base (26) of the retentate chamber (21) slopes down on one side laterally.