Microfabricated arrays of immobilized oligodeoxynucleotide probes are proving to be a powerful tool for rapidly generating sequence data via hybridization. These arrays are made either by immobilization of the probe post-synthetically, or by in situ synthesis of the probe. Hybridization of the target is easily achieved on the arrays, with analysis proceeding either by direct detection, or through enzyme-mediated detection; analysis of the hybridization pattern yields sequence information about the target. Such facile and rapid data acquisition will assist the challenging task of sequencing the human genome, and also will lead to a new generation of diagnostic assays.