Heavy metal stress adversely affects plant growth and productivity worldwide. Alleviating the stress effect through the exogenous use of various chemical substances has become an interesting area of study in the field of plant stress tolerance. As a thiol compound, the cysteine derivative N-acetylcysteine (N-acetyl-L-cysteine, NAC) is the precursor of glutathione synthesis and a potent ROS scavenger with powerful antioxidant and free radical scavenging capabilities. This study investigated the effects of heavy metals (Cd, Hg and Pb, 100 mu M) on accumulation of soluble sugars and polyamine content in roots and shoots of wheat seedlings, the water potential and proline content in shoots and the role of NAC in protection against heavy metal toxicity. The addition of 1 mM NAC significantly increased root content of glucose, fructose and sucrose in varying degrees (avg. 1.34-, 1.20- and 1.51-fold, respectively) in comparison with heavy metals alone. The treatments led to a significant reduction of sugar content in shoots. Water potential values were highly correlated with proline and sugar content in wheat seedling shoots. Heavy metal stress significantly reduced polyamine content in both plant parts. The addition of NAC increased polyamine content in seedlings in comparison with heavy metals alone in both roots and shoots. These results suggest that NAC may protect plants from oxidative stress damage in heavy metal stress, and this enhancement of stress tolerance seems to involve soluble sugar and polyamine biosynthesis.