The purpose of this experiment was to determine whether genotypic differences in photosynthetically water use efficiency (WUEg) and other gas exchange traits exist in 12 durum wheat genotypes, included six local cultivars from South-eastern Anatolia. Flag leaf gas-exchange measurements were performed on well-watered and fertilized field grown plants, which were planted after vernalization. Weather conditions during measurement were suitable for high transpiration. At anthesis no genotypic variation was observed for water use efficiency, calculated using leaf conductance (WUEgs). The results indicate that measurements for WUEg should be performed during development under different environmental conditions to partially overcome difficulties caused by developmentally and environmentally induced variation.