Abstract: The changes in content and form of polyamines(PAs) in the leaves of two soybean (Glycine max L.) cultivar seedlings differing in drought tolerance were investigated with HPLC under osmotic stress.Yudou No.24 cv.(drought-tolerant) showed higher increases magnitude in free-spermidine(fSpd) and free-spermine(fSpm) in leaves than Yudou No.6 cv.(drought-sensitive) after treated with polyethylene glycol(PEG) 6,000 for 7 d,while Yudou No.6 cv.showed a higher increased magnitude in free putrescine(fPut).Thus Yudou No.24 cv.gave a higher ratio of(fSpd + fSpm) / fPut than Yudou No.6 cv.in leaves under osmotic stress.Exogenous treatment of seedlings with methylglyoxal-bis(guanylhydrazone)(MGBG),an S-adenosylmethionine decarboxylase(SAMDC,which catalyzes the Spd and Sam biosynthesis) inhibitor,resulted in a reduction of fSpd and fSpm in leaves and aggravation of PEG-induced injury to Yudou No.24 cv.seedlings,while exogenous Spd treatment resulted in an increase in fSpd + fSpm in leaves,furthermore retarded PEG-induced injury in Yudou No.6 cv.seedling.There was no statistically significant difference between the contents of acid soluble covalently conjugated PAs(ASCC-PAs) in leaves of both cultivars under PEG osmotic stress,suggesting that the level of ASCC-PAs in leaves had no relationship with the osmotic stress tolerance of wheat seedlings.Osmotic stress induced a significant increase in acid insoluble covalently conjugated polyamines(AISCC-PAs) level in seedling leaves of Yudou No.24 cv.,whereas it had a slightly influence on AISCC-PAs in Yudou No.6 cv.seedlings.Exogenous treatment of seedlings with phenanthrolin(o-Phen),an inhibitor of transglutaminase(TGase,which catalyzes AISCC-PAs biosynthesis),also aggravated PEG-induced injury to Yudou No.24 cv.seedlings,combined with a decrease in AISCC-PAs levels.The results suggested that fSpd,fSpm and PIS-Pas,which strengthened the osmotic stress tolerant capacity of soybean seedlings.