An improved procedure for preparing PCR cloning vectors was developed. This procedure includes the incorporation of adapters to create XcmI restriction enzyme sites in pBluescript II SK(+) vectors, digestion with XcmI followed by further digestion of the small fragment produced by XcmI digestion with additional enzymes, and purification with PCR purification kits. Using this procedure, PCR cloning vectors with high ligation efficiencies and low blue or false-positive colonies were obtained.