A method to purify genomic DNA from "Escherichia coli" is presented. The method is an amalgam of published methods but has been modified and optimized for use in the undergraduate biochemistry laboratory. Specifically, the method uses Tide Free 2x Ultra laundry detergent, which contains unspecified proteases and lipases, "n"-butanol, 2-propanol, ethanol, and ribonuclease A (or 8 mM sodium hydroxide), and requires a minimum of specialty equipment. Because a number of the required reagents are readily attainable from retail stores, the cost is low enough to allow each student to prepare a sample of purified genomic DNA, even in large laboratory classes. By following the protocol, students are able to purify genomic DNA and use this genomic DNA as a template for a polymerase chain reaction in one 3-h laboratory period. (Contains 3 figures and 3 notes.)