Fluorescein-12-dUTP (fluorescein-5(6)-carboxaminocaproyl-[5-{3-aminoallyl}-2'-deoxyuridine-5’-triphosphate]) is designed for enzymatic nonradioactive labeling of DNA during cDNA synthesis, PCR, nick-translation, random primed labeling, or primer extension. The nucleotide can be incorporated into DNA with the enzymes like reverse transcriptases, Taq DNA polymerase, phi29 DNA polymerase, Klenow fragment or DNA Polymerase I.