A base-flipping phenomenon has been established for DNA methyltransferases and for DNA base-excision repair glycosylases and is likely to prove general for enzymes that need access to DNA bases to undergo chemical reaction. T4 phage beta-glucosyltransferase (BGT) is a good candidate for this novel mechanism. In order to confirm this, BGT was crystallized with an abasic site-containing DNA and uridine diphosphoglucose (UDP-glucose). The crystallization strategy is described. A complete data set was collected at 1.8 A resolution on a Cu Kalpha rotating-anode X-ray source. Molecular replacement was performed and the initial electron-density maps clearly show bound DNA.