The microarray scanner measures the fluorescence intensity of labeled sample nucleic acid (DNA and RNA) bound to microarrays. Its ability to measure fluorescence from two dyes simultaneously facilitates all two-color microarray studies. This technology provides for rapid, high-quality, automated scanning of microarrays. The microarray scanner uses two lasers, a SHG-YAG laser (532 nm) and a helium-neon laser (633 nm). The lasers excite Cyanine-3 (Cy-3) and Cyanine-5 (Cy-5) labeled RNA or DNA to measure fluorescence after hybridization of the target nucleic acid to the microarray probes. The microarray scanner is optimized for high signal-to-noise performance in the Cy-3 (550—610 nm) and Cy-5 (650—750 nm) emission bands, with a wide dynamic range (up to five orders of magnitude) and low spectral cross-talk. This allows for measurement of a very broad range of target concentrations and for higher data confidence at lower signal levels. The laser excitation is scanned rapidly back and forth across the microarray. Fluorescence from the labeled samples is converted to an electrical signal by a high-performance PMT. Very low noise amplifiers and digital integrators process the PMT signal into a digital measurement that is recorded.