Protocol for preparation of DNA for pulsed-field gel electrophoresis: isolation of DNA from mammalian cells and tissues. Genomic DNAs from mammalian cells are prepared for pulsed-field gel electrophoresis by lysing cells in situ in an agarose plug. Following digestion with an appropriate restriction enzyme, the plug is loaded directly into the well of a pulsed-field gel or it can be melted before loading.