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ABSTRACT A portable eddy correlation system was used to make direct, real-time mfeasurements of evapotranspiration over irrigated alfalfa. T^e surface energy balance equation was used to evaluate system performance, with the closure ratio defined as the ratio of the sum of latent and sensible heat fluxes to the sum of net radiation and soil heat flux. For six 24-hour periods, the mean uncorrected closure ratio was 0.85. After corrections were made for sensor separation, the mean closure ratio improved to 0.95. Measurements were made during several other periods, however, sensor malfunctions resulted in erroneous data during these periods. Care was required in deploying and maintaining the instruments, but the system proved to be a viable alternative for making real-time evapotranspiration measurements with portable equipment. KEYWORDS. Evapotranspiration, Eddy correlation. Irrigation, Measurement, Sensors.