Field experiments were conducted over two seasons (2005-06 and 2006-07) using six durum wheat genotypes varying in grain carbon isotope discrimination ([Delta]) but similar in phenology. Experimental sites at Tel Hadya, Breda, Muslmieh and Yahmoul across rainfall zones in Northern Syria were used. The main objective of this study is to relate the wheat yields of the different genotypes with [Delta] and other plant traits. Plant growth was monitored throughout the growing season. [Delta] was measured for every plot in the grain ([Delta]G) and the 4th fully expanded leaf ([Delta]L). Also, ash and protein contents of grain were analyzed. Soil water content throughout the growing season was measured at some sites to calculate water use. Yield variability between sites was mostly due to rainfall, with variability between cultivars within a site being due to season. [Delta]L was higher, with no stress evident at this stage, compared with [Delta]G. [Delta]L, ranging from 19.97 to 22.76[per mille sign], was lower at the drier sites and higher at the wettest site, which changed to the opposites for [Delta]G ranging from 12.88 to 16.62[per mille sign]. Positive correlations were found between [Delta] and yields of grain and biomass. The stronger correlations were at the drier sites, whilst at the wettest site there was no significant relationship. [Delta]L for the different genotypes was more stable between sites and seasons than [Delta]G. Water use efficiency did not differ between genotypes, unlike [Delta]. [Delta] was also correlated to grain ash and protein content. This suggests to use these cheap and easily obtainable plant traits as surrogate if [Delta] was unavailable.