In subtractive hybridization, target sequences in the tester are enriched by hybridizing with an excess amount of driver, followed by removing the tester hybridized with the driver. All of existing subtractive cloning methods are designed to remove the tester/driver hybrid. The removal of hybrid, however, is often unsatisfactory For various reasons. In this study we developed a subtractive enrichment protocol in which the tester/driver can be completely removed by selecting only the tester/tester after hybridization. In this protocol both the tester and driver DNAs are ligated with same linker DNAs and amplified by polymerase chain reaction (PCR). The tester DNA is then digested with two different enzymes and used in subsequent hybridization with an excess driver. After hybridization, the DNA is ligated with the adaptor that is only compatible with the tester/tester. Since only the tester/tester can have the new adaptor, no tester/driver can be amplified by PCR in this protocol. Unlike other methods, a 100% subtraction efficiency can be achieved even though the enzymatic treatments used in the enrichment procedure are incomplete. Furthermore, only the hybridized tester DNA can have the new adaptor and be amplified by PCR, resulting in 100% denaturation in effect. The efficacy of this novel method was verified with the model system in which a known amount of the target sequence is included.