Abstract: A method for identification of the most abundant oligonucleotide species in a library of oligonucleotides comprising more than 106 oligonucleotide species, wherein the oligonucleotides of the library of oligonucleotides are not inherently capable of exponential amplification by PCR and include a coding sequence, which is characteristic of one oligonucleotide specie of the library of oligonucleotides and only one fixed sequence, which is present in a plurality of oligonucleotide species of the library of oligonucleotides, said fixed sequence being located on a 5? side of the coding sequence, and wherein the method comprises specifically amplifying the sequence of a hybridised oligonucleotide species using the steps of: incubating the library of oligonucleotides under conditions of hybridization such as to allow complementary coding sequences to hybridize and form hybridized oligonucleotide species; extending a 3? end of one or more of the hybridised oligonucleotide species, having only one fixed sequence, to p