Concurrent measurements of the fraction of photosynthetically active radiation intercepted by vegetation canopies, FIPAR, and ground-, helicopter-, and satellite-based reflectance measurements were taken at 13 tallgrass praire sites. The sites were subjected to various combinations of burning and grazing mangements. The ground- and helicopter-based reflectance measurements were taken on the same day or within a few days of the time the Landsat and SPOT satellites passed over the sites. Sun photometer readings taken at the times of the satellite overpasses were used to correct for atmospheric attenuation. Hand-held radiometer spectral indices were strongly correlated with the helicopter-based values (r=0.94) for Landsat thermatic mapper (TM) and 0.86 for SPOT). However, the ground-, the helicopter-, and the satellite-based normalized difference spectral vegetation indices showed low sensitivity to changes in FIPAR. Reflectance measurements were only moderately well correlated with measurements of FIPAR (r=0.82 for the hand-held radiometer, 084 for helicopter measurements, 0.75 for SPOT, and 0.73 for the Landsat TM). Improved spectral indices that can compensate for site differences are needed to monitor FIPAR more reliably. ¿American Geophysical Union 1992