DNA affinity chromatography has been used for the purification of polynucleotides and polynucleotide-binding proteins, including restriction endonucleases, polymerases, proteins involved in recombination, and various transcription factors (reviewed in [1 ,2 ]). The earliest supports used were DNA celluloses. P. T. Gilham pioneered the chemical synthesis of homopolymeric DNA-celluloses such as oligo dT cellulose and their use for purifying polynucleotides, especially polyA mRNA, by hybridization (3 ). Later, Alberts, Litman, and their coworkers adsorbed DNA to cellulose to purify DNA-binding proteins (4 ,5 ). Arnt-Jovin and colleagues (6 ) attached DNA to agarose and Kadonaga and Tijan (7 ) introduced the addition of competitor DNA to the mobile phase to lessen nonspecific binding. Various other laboratories have attached DNA to Teflon fibers, latex beads, magnetic particles, and other media for DNA affinity chromatography (reviewed in ref. 1 ).