Method of choice when large amounts of mammalian DNA are required, for example, for Southern blotting (Rapid Isolation of Mammalian DNA, Rapid Isolation of Yeast DNA, Southern Blotting: Capillary Transfer of DNA to Membranes) or for construction of genomic libraries in bacteriophage {lambda} vectors. Approximately 200 µg of mammalian DNA, 100-150 kb in length, is obtained from 5 x 107 cultured aneuploid mammalian cells (e.g., HeLa cells).