RESPONSE of Triticum aestivum (cv. Giza 168) to drought ……...stress and the application, of the inevitable protective effect of exogenous application of trehalose was investigated. Drought reduced the plant growth parameters (dry weights, area of leaves) and photosynthetic pigments. Conversely, drought caused an increase in the levels of proline, lipid peroxidation, peroxidases and endogenous trehalose. The levels of endogenous IAA and GA3 were decreased in drought-stressed plants, however the level of ABA was increased by more than 3-fold of control plants. Specific activity of trehalose -6- phosphate synthase, which is one of the two enzymes that participates in synthesizing trehalose in plants by the production of trehalose-6-phosphate; was increased by 3-fold of control in root of the drought-stressed plants. On the other hand, the specific activity of trehalase was drastically decreased. Pre-treatment of wheat plant with 40 mM trehalose -by irrigation- improved the above mentioned morphological and physiological parameters to retained them almost near the control. Thus, pre-treatment with 40 mM trehalose alleviated the harmful effect of drought stress on the test wheat cultivar.