A pre-amplification reaction mixture for selective amplification of one or more target nucleic acid sequences, said reaction mixture comprising: a tagged oligonucleotide comprising first and second regions, said first region comprising a target hybridizing sequence hybridized to a target region contained at a 3'-end of one or more target nucleic acid sequences present in said reaction mixture and said second region comprising a tag sequence situated 5' to said target hybridizing sequence; a first oligonucleotide comprising a hybridizing sequence which hybridizes to a 3'-end of the complement of one or more of said target nucleic acid sequences; and a second oligonucleotide comprising a hybridizing sequence which hybridizes to the complement of said tag sequence, wherein said reaction mixture is substantially free of an active form of said tagged oligonucleotide which is not hybridized to said target region contained in said one or more target nucleic acid sequences present in said reaction mixture, wherein said active form of said tagged oligonucleotide has an available target hybridizing sequence for hybridization to said target region present in a non-target nucleic acid added to said reaction mixture, and wherein said reaction mixture does not comprise a nucleic acid polymerase capable of extending any of said oligonucleotides in a template-dependent manner.