CHEF genomic DNA plug kits provide a convenient means for preparing intact, chromosome-sized DNA for PFGE. With such large molecules, pipetting mechanically shears the DNA, resulting in unacceptable quality for PFGE separations. This problem has required procedures for lysis and deproteinization of whole cells embedded in agarose to yield intact purified DNA. Three kits are available for the preparation of bacterial (lysozyme-sensitive) or mammalian genomic DNA and yeast chromosomes (YACs). Each kit contains all the enzymes, reaction buffers, and restriction digest-qualified CleanCut agarose necessary to prepare 100 plugs, as well as disposable plug molds and screened caps for simplified plug processing. Each kit is thoroughly tested to ensure that prepared genomic DNA can be restriction digested and separated on a CHEF electrophoresis system.