Plant expression cassettes containing the Escherichia coli cysE gene alleles (encoding SAT) were constructed. After the Agrobacterium-mediated transformation of tobacco, we identified stable transformed plants containing several-fold higher SAT activity in comparison to the control plant. Determination of non-protein thiol contents indicated two- to threefold higher cysteine and glutathione levels in some of these transgenic plants. The maximal elevation of the cysteine level was about fourfold while that of GSH was about twofold higher than in the controls. The most striking physiological consequence of the modification of sulfur metabolite levels in the transgenic plants, however, was their several-fold increased resistance to oxidative stress generated by exogenous hydrogen peroxide.