Biotin-14-dATP is a dATP analog which contains biotin attached at the 6 -position of the purine base by a 14-atom spacer arm. The biotin - labeled nucleotide is incorporated into DNA by nick translation in the presence of the deoxynucleotide triphosphates dTTP, dGTP and dCTP. Other labeling procedures (i.e., homopolymer, tailing with a terminal deoxynucleotidyl transferase, replacement synthesis with T4 DNA polymerase or random primed synthesis) may be satisfactory. The biotin-labeled DNA can be detected colorimetrically using Steptavidin-Alkaline Phosphatase Conjugate and NBT/BCIP or by chemiluminescence, using streptavidin alkaline phosphatase and an appropriate chemiluminescent substrate.