An optical multichannel analyzer was used to develop a reflectance radiometer for measurement of medical diagnostic samples. Sample areas were small, typically 5 mm x 5 mm. Spectral and temporal resolution of the reflectance measurements were 0.5 nm and 17 ms, respectively. Reflectance drifts were found to be less than 0.004 over 2 h with accuracy better than 0.012 compared with a reference method. Flexible instrument design allows use of many different illumination and detection geometries. Applications include performance evaluations of chemical formulations and readhead designs.