Water stress, which limits the distribution and productivity of durum wheat (Triticum durum Desf.) in the Mediterranean region, is also considered to be a major factor reducing yield in semiarid regions. Improving drought resistance is thus an important objective in plant breeding programs for rainfed agriculture. The current study was carried out to identify drought-tolerant durum wheat lines among 10 lines and one variety (Douma1, the control) in the first and second settlement zones in the Southern part of Syria and to recognize the most important physiological parameters associated with drought tolerance. Membrane stability index, chlorophyll (chl) content, relative water content and chl fluorescence were recorded at the vegetative and anthesis stages, as were yield and yield components. Data recorded at vegetative and anthesis stages in both zones showed that there were significant differences between all lines growing in the first and second settlement zones and that all characters in the second zone were significantly lower than those in the first zone. Line 1 was superior to Douma1 in terms of membrane stability index, relative water content, chl content and chl florescence, also showing better yield and higher total plant biomass, tiller number/m2, 1000 grain weight and grain number/ear than the control. The ability of wheat cultivars to perform reasonably well in variable rainfall and water-stressed environments is an important trait since it allows for stable production under drought stress. Moreover, prior to genetic manipulation, it is important to characterize the physiological parameters of known drought-tolerant or drought-sensitive wheat cultivars with the objective of better understanding their physiological responses under drought

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