Device for the isolation of nucleic acids from a liquid sample by introducing the liquid into the device through an inlet opening and passage of the sample through a nucleic acid binding material and discharging of the resulting liquid through an outlet opening, wherein the nucleic acid binding material is inserted through the outlet opening during the manufacture of the device and the outlet opening is narrowed in order to hold the material. The device is particularly simple and reliable to manufacture but yet ensures that nucleic acids can be isolated without contamination.