Many genes expressed in the human genome have not been identified despite intensive efforts. We observed that the presence of long poly(dAydT) sequences in the 3* end of cDNA templates contributes significantly to this problem, because the hybrids formed randomly between poly(dA) and poly(dT) sequences of unrelated cDNA templates lead to loss of many templates in the normalizationysubtraction reactions. The low abundant copies, which account for the majority of the expressed genes, are affected in particular by this phenomenon. We have developed a strategy called screening poly(dAydT)2 cDNAs for gene identification to overcome this obstacle. Applying this strategy can significantly enhance the efficiency of genome-wide gene identification and should have an impact on many functional genomic studies in the postgenome era.