Productivity change is one of the most important sources of agricultural production growth and much time has been devoted to the study of measures of productivity growth as well as the estimation of productivity changes in agriculture. Much of the literature in the area, however, has focused on agriculture as a whole or on partial productivity for individual crops. In the area of the measurement of total factor productivity on individual crops, little work has been done. The general concern of this study is to help fill this gap. Emphasis is placed on the measurement of productivity levels for individual crops when some input data are unavailable. Also, the comparison of productivity changes among crops is considered;The first objective of this study is to measure total factor productivity changes for individual crops. The duality between production and profit function is used to derive an equation for production that depends on input quantities when data are available and input prices when data are not available. The proposed model is estimated using data for four U.S. field crops--corn, cotton, soybeans and wheat in the period of 1949 to 1982. Total factor productivity has grown at a rate of 3.36% for corn, 2.40% for soybeans, 2.04% for wheat, and only 1.33% for cotton over the period;The second objective is to compare productivity changes among crops. An absolute productivity index which considers both changes in total factor productivity and changes in value of outputs and inputs is proposed in the study. The proposed model is based on the concept of opportunity cost in that the value of current output is compared to the cost of production that would be occurred if there has been no technical change. Sectors with large values of output relative to these shadow costs are said to have high levels of absolute productivity;Indexes of absolute productivity were calculated for each crop. The index was highest for corn at 1.95% and lowest for cotton at 1.10%. Absolute productivity in wheat grew at 1.15% while soybeans productivity grew at 1.17%.