The report describes instrumentation, methods, and preliminary results for a study on evapo- transpiration at a grassland in Snively Basin of the Arid Lands Ecology Reserve. Instrumentation was used to collect data from May 30 to October 15, 1990. A combination of the Bowen-ratio and Penman-Monteith methods was used to calculate estimates of evapotranspiration. The Bowen-ratio method could be used to calculate estimates of latent-heat flux and evapotranspiration during only parts of the study period. Latent-heat flux values obtained during these periods were used in the Penman-Monteith method to estimate the canopy resistance. These canopy resistances were averaged for each day and the average values were used to recalculate the laten-heat flux for all periods using the Penman-Monteith method. The canopy resistance ranged from near zero during periods of rainfall to more than 40,000 seconds per meter during periods of extreme dryness. Evapotranspiration estimates varied during the study period. Daily evapotranspiration ranged from less than 0.1 millimeter on some days in August, September, and October to about 2 milli- meters on June 3 and August 22. Monthly totals of evapotranspiration were as follows: June, 28.2 millimeters; July, 10.5 millimeters; August, 15.0 millimeters; September, 5.3 millimeters; and October 1-15, 1.8 millimeters. Evapotranspiration values given in the report are estimates. Some error, perhaps as low as 25 percent on a daily basis and 4 percent on a monthly total basis, is probably introduced into these estimates through complexities of data collection, data analysis, and canopy-resistance estimation, particularly when evapotranspiration was near zero.