Miniaturized sample formats offer advantages in cost and throughput to screening laboratories. Imaging systems may be valuable tolls for assay miniaturization. We describe fluorescence performance of our TundraTM assay imaging system, which incorporates a thinned, back illuminated CCD area detector, a telecentric lens with internal excitation optics, and AssayVisionTM software. Using a flat field correction, Tundra imaged a difficult (faint) gel with performance similar to that of a high performance scanning laser. The accuracy of Tundra's dedicated well plate calibration functions was also evaluated in 384 (40 (mu) l sample volume) and 1536 (5 (mu) l) well plates, and across a realistic range of fluor concentrations. With both plate formats, and across the full range of fluor concentrations, Tundra shows coefficients of variation which are similar to those of a scanning laser, and to those reported for PMT devices. Tundra also exhibits highly linear response to fluor concentration.