Technical Abstract: The ability of plants to convert transpiration into dry matter has been studied since the early 20th century. Research has compared differences among species using transpiration efficiency (TE), the ratio of biomass yield (Yb) to transpiration (T); and m and k, which are the slopes of the linear Yb/T relationship normalized by atmospheric evaporative demand. The objective of this research was to develop transpiration and biomass relationships (TE, m, and k) and the transpiration and grain relationship (TEg) of grain sorghum (Sorghum bicolor L. Moench) grown in a field environment. Grain sorghum was grown in 1998 and 1999 in weighable lysimeters using stored soil water only and in a rain shelter facility. This approach limited the irrigation and precipitation evaporation components of E so that T estimated (Test) using lysimetry in a field environment was emphasized. The TE remained constant through a range of water availability. The TE was similar between the two years, and the combined data produced a slope of the Yb/Test relationship of 3.5 g m**-2 mm**-1. This was similar to the 3.3 g m**-2 mm**-1 reported for sorghum in the early 20th century, but smaller than current field studies which ranged from 4.0 g m**-2 mm**-1 to 5.7 g m**-2 mm**-1. The TEg was 2.6 g m**-2 mm**-1. Normalization of Test by seasonal averages of reference evapotranspiration and vapor pressure deficit produced significant differences between years in the slopes of the relationships. Transpiration efficiency did not require normalization for variations in climate between years.