Spectral reflectances of several crops at Phoenix, Arizona were measured during two growing seasons using a hand-held radiometer, the Exotech Model 100A, that had a spectral bandpass configuration similar to scanning radiometers aboard Landsat 2 and 3. During the period of grain filling, yields of two wheat and one barley variety were well correlated with the integrated daily values of a modified vegetation index derived from reflectances in MSS Bands 5 and 7 (0.6-0.7 and 0.8-1.1 μm respectively). The derived model accounted for 88 per cent of the variability in yields from 103 to 656 g/m2which were due to differential experimental soil moisture conditions (20 to 70 cm applied water).