Wheat stem reserves can be an important contributor to grain filling particularly under drought conditions. Knowledge concerning genetic variation in stem reserve could be empolyed to develop wheat genotypes more adapted to harsh environments. The aim of this research was to study the ability to store assimilates in stem and their re-mobilization to the grain in all the 81 Iranian wheat cultivars. The plant materials were evaluated using two simple lattice designs with two replications under irrigated and drought conditions at University of Tehran Research farm during 2007-2008. Drought stress was imposed by the plants being withheld from being watered at the heading stage. The level of dry matter stored and mobilized was estimated by measurement of changes in masses of internodes from anthesis to maturity at 8 day intervals. Relationships among internodes' length as well as specific weight and accumulation and re-mobilization of stem reserves were determined. The results revealed that dry weight of lower internodes was higher than that of the upper ones. Maximum release of stored carbon, on the average, was found in lower internodes followed by penultimate and peduncle. Release of dry matter from internodes was decreased by drought stress in some cases, while in some other cases the reverse trend was observed. The same pattern was observed for re-mobilization efficiency. Relationship among internodes characteristics and accumulation and re-mobilization were not the same for stem segments and in all experimental conditions. Release of dry matter from internodes was not correlated with grain yield in well watered conditions. Dry matter mobilized from lower internodes was significantly correlated with grain yield in drought affected plants. Significant genotypic variation for accumulation and re-mobilization was observed under both conditions indicating that these traits can be advantageously manipulated in breeding programs.