Isolation of DNA segments adjacent to known sequences is a tedious task in genome-related research. We have developed an efficient PCR strategy that overcomes the shortcomings of existing methods and can be automated. This strategy, thermal asymmetric interlaced (TAIL)-PCR, utilizes nested sequence-specific primers together with a shorter arbitrary degenerate primer so that the relative amplification efficiencies of specific and nonspecific products can be thermally controlled. One low-stringency PCR cycle is carried out to create annealing site(s) adapted for the arbitrary primer within the unknown target sequence bordering the known segment. This sequence is then preferentially and geometrically amplified over nontarget ones by interspersion of high-stringency PCR cycles with reduced-stringency PCR cycles. We have exploited the efficiency of this method to expedite amplification and sequencing of insert end segments from P1 and YAC clones for chromosome walking. In this study we present protocols that are amenable to automation of amplification and sequencing of insert end sequences directly from cells of P1 and YAC clones.