The PowerWave XS Microplate Spectrophotometer is a single channel absorbance microplate reader that has the capability of measuring absorbance in 96- and 384-well microplates (Figure 1). This monochromator-based instrument, which has a wavelength range of 200-999 nm, requires no filters and can perform spectral scans of substances in increments as small as 1 nm. A Xenon-Flash lamp is used to illuminate a high precision diffraction grating monochromator. The monochromatic light is then split into experimental and reference channels. The experimental channels are then focused onto the microplate, while the reference channel is directed to the dedicated reference silicon diode detector. After passing through the experimental sample, unabsorbed light is focused onto silicon diode detectors. Elevated temperatures are regulated by a four-zone control system that assures superior temperature uniformity up to 68°C.