Nucleic acid hybridization with labeled probe sequences is a well known analytical tool used in molecular and cell biology. The utility of hybridization has been greatly increased by the development of in vitro methods for incorporation of label (either isotopic or nonisotopic) into the nucleic acid probe molecules. One of these methods is nick translation, where nucleotides are incorporated into double stranded DNA by DNA Polymerase 1 at sites where the molecule has been nicked by DNAse 1. Nucleotide mixes containing a label 32P-dATP or Fluorescein-dUTP) provide the pool of nucleotides which DNA Polymerase 1 will incorporate into the double stranded DNA molecule. The excess labeled nucleotides are then separated from the finished, "labeled" DNA.