Protocol for restriction endonuclease digestion of DNA in agarose plugs. Genomic DNA isolated from mammalian, yeast, or bacterial cells can be digested with restriction endonucleases by incubating agarose plugs containing the DNA in the presence of the desired enzyme. After digestion, the DNA can be fractionated by pulsed-field gel electrophoresis and either isolated from the gel or analyzed by Southern Hybridization.