A flow filter for separating blood into plasma and cellular constituents comprises a filter housing, which has a blood delivery line, a plasma removal line and a cell removal line, a fine-pore membrane, which comprises a bundle of parallel hollow fibres arranged in the filter housing, has an inflow end connected to the blood delivery line and which divides the filter housing into a first flow chamber that is connected to the cell removal line and a second flow chamber that is connected to the plasma removal line. The filter also comprises a pressure-adjusting device for adjusting the pressure in the hollow fibres, said device being connected to an outflow end of the bundle.
