The canopy and air temperature difference (T(c)-T(a)) usually becomes more negative as canopy leaf area and crop cover increase. The increasingly negative value of T(c)-T(a) in the context of an energy balance for the crop canopy can be related to an increase in the system's aerodynamic resistance or a decrease in canopy resistance. In 1983 and 1984, the slope of the nonstressed baseline increased as crop cover increased; however, in 1985, this trend was not observed. If the change in slope of the nonstressed baseline among years is not the same as plant leaf area increases, this indicates that the system's resistance is different. CWSI values for the days of nonlimiting soil moisture indicate that mid-day values of canopy resistance were about 50 s/m for crop cover between 30 and 90 percent for all years. Thus, the aerodynamic resistance is most likely varying and causes the difference in the pattern of nonstressed baseline slopes among years as crop cover changes. Mean crop water stress index (CWSI) values were computed by averaging weekly values obtained at 1 1/2 hours past solar weekly values obtained at 1 1/2 hours past solar noon. Mean CWSI values for the period from first bloom until initial boll opening displayed a common relationship with lint yield for all years.