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Temporal variation in earth-atmosphere system reflectance in the 0.5-1.1 [mu]m wavehand was determined from Landsat MSS data for an area of and rangeland in south-central New Mexico. Data were extracted from eight MSS scenes for the period 1973-1983, with four scenes from 1976. Maximum potential change between the extremes of rangeland degradation status was estimated to provide a benchmark for assessing the significance of the observed variations. Reflectance standardized for differences in sensor radiometric response by ERIM coefficients increased significantly from 1973 to 1983, but standardization by Landsat Data Users Handbook coefficients resulted in little long-term change. Short-term ( > 1 year) variation was significant relative to maximum potential change. A sequence of three Landsat-2 scenes within one year showed a decrease in reflectance with increasing solar zenith angle. The effect of zenith angle on shading of the soil surface by plants (" protrusions effect" of Otterman) was estimated and found to be about the same magnitude as the observed within-year variation in reflectance with solar zenith angle.