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Taking wheat cultivars drought-resistant Luohan-6 and drought-sensitive Zhoumai-18 as test objects, their seedlings ammonium assimilation enzyme activities and related parameters were determined under osmotic stress. The plant biomass had an obvious decrease under osmotic stress, with a larger decrement for Zhoumai-18 than Luohan-6. Osmotic stress increased the plant ammonium content, especially for Zhoumai-18. The glutamine synthetase (GS) activity varied with wheat cultivars. For Luohan-6, the GS activity increased significantly under low osmotic stress but decreased under high osmotic stress; while for Zhoumai-18, the GS activity decreased with increasing osmotic stress. The NADH-dependent glutamate dehydrogenase (NADH-GDH) increased with increasing osmotic stress, with a marked increment under low osmotic stress for Zhoumai-18, and under high osmotic stress for Luohan-6. The NAD+-dependent glutamate dehydrogenase (NAD+-GDH) and NADP-dependent isocitrate dehydrogenase (NADP-ICDH) activities also increased with increasing osmotic stress, with a greater increment of NAD+-GDH activity for Zhoumai-18, and of NADP-ICDH activity for Luohan-6. It was suggested that the increased drought resistance of wheat plants could be related to the increased ammonium assimilation resulted from the enhanced GS and NADH-GDH activities under low and high osmotic stress, respectively. [ABSTRACT FROM AUTHOR]