Devices and techniques for hybridization of nucleic acids and for determining the sequence of nucleic acids. Arrays of nucleic acids are formed by techniques, preferably high resolution, light-directed techniques. Positions of hybridization of a target nucleic acid are determined by, e.g., epifluorescence microscopy. Devices and techniques are proposed to determine the sequence of a target nucleic acid more efficiently and more quickly through such synthesis and detection techniques.
 The invention described herein arose in the course of or under Contract No. DE-FG03-92ER81275 (Grant No. 21012-92-II) between the Department of Energy and Affymax; and in the course of or under NIH Contract No. 1R01HG00813-01.