A mixture of random nonanucleotides used to prime DNA synthesis in vitro along multiple sites of denatured template DNA (1). The primer-template complex is a suitable substrate for DNA Polymerase I (Klenow Fragment). The newly synthesized complementary DNA is “oligo-labelled” by substituting any radiolabeled nucleotide for the appropriate non-radioactive nucleotide in the reaction mixture. Use of synthetic d(N9) primer ensures the presence of virtually all sequence combination of nanomer primers which results in equally labelled DNA of high specific activity (1,2).