The method of enzyme-linked immunosorbant assay(ELISA) was employed to determine the changes of abscisic acid(ABA),indoleacetic acid(IAA),gibberellin(GA_3) and zeatin(iPA) contents in flue-cured tobacco roots and leaves under osmotic stress.The results showed that leaf water potential declined and leaf protein content increased under osmotic stress.It was also found that the content of ABA and iPA in the roots and leaves was increased and that of IAA and GA_3 was decreased significantly.Lower leaf water potential and ABA content and higher content of protein and IAA,GA_3,iPA in the leaves of plants treated with solute osmotic potential at-0.5 MPa was observed as compared to those with solute osmotic potential of-0.25 MPa.Moreover,the time was shorter for the former treatment when iPA content in roots and ABA content in leaves reached the peak,while GA_3 concentration in roots declined to the valley.However,the changes of the other indices in roots and leaves were synchronous.The results also showed that the decrease of IAA and GA_3 content in the roots was more significant and the increase of ABA content was more rapid as compared with the leaves at the early stress stage(6 h).It suggested that the response of endogenous phytohormones in flue-cured tpbacco roots to osmotic stress was more susceptible than that in the leaves.