The term pulsed-field gel electrophoresis (PFGE) is used as an acronym to indicate any technique that resolves (large) DNA molecules by continuous reorientation. It bridges the resolution gap between cytogenetic methods (> 5 Mb) and DNA analysis (< 50 kb). Initially, PFGE was used to study the chromosomal content of unicellular eukaryotic organisms of interest to genetic research and population health. Later, PFGE was used to construct megabase maps of segments of the human genome. Successfull utilization of PFGE requires the availability of very high-molecular weight DNA. This article describes the modification of standard DNA protocols necessary to handle large DNA molecules, based on its encapsidation in agarose.