A DNA isolation method by removal of constituents, interfering with a subsequent PCR is disclosed. According to an embodiment of the method, all substances and method steps are fully integrated into a closed unit (cartridge) for single use, which allows entry of a DNA-containing sample and DNA-binding substrates are used for isolating the released DNA. In particular, when the method is applied to DNA isolation from whole blood by disruption of white blood cells, the reagents, required for carrying out the cell disruption and other reactions, are stored in a form which is stable at room temperature. For disrupting the white blood cells and for DNA isolation, a dry stored lysis reagent is dissolved in an aqueous solution and brought into contact with the white blood cells. The corresponding assembly includes a unit, for housing DNA-containing biological containers and/or reagents, whereby at least one microchannel is provided to contain reagents, whereby the reagent is present in the microchannel as a dry mixture with a negligible vapor pressure, which forms a stable substance at room temperature.