A rapid change in gene expression in plants in response to stress is important for environmental adaptation. An mRNA differential display technique was used in this study to analyze alterations in gene expression in Lepidium sativum in response to different concentrations of lead. The relationship of differential expression patterns to the identification of cDNAs induced during lead toxicity was determined. Polymorphism was detected under lead toxicity and the differentially expressed genes in stressed seedlings were strongly and rapidly induced under higher lead concentrations (400 and 600 ppm), whereas induction was delayed and transcripts accumulated to a lower level under lower concentrations (100 and 200 ppm). A great variation in isoforms of different antioxidant enzymes, e.g. superoxide dismutase (SOD; EC126.96.36.199), catalase (CAT; EC188.8.131.52.) and ascorbate peroxidase (APx; EC184.108.40.206) were detected in response to lead treatments. Lead toxicity increased lipid peroxidation and reactive oxygen species (ROS) generation especially at higher concentrations, but the increase was significantly lower at lower concentrations. The results obtained indicate that the pattern of antioxidant isozymes are affected upon exposure of L. sativum seedlings to lead and the variations are concentration dependent. Within such response patterns, gene expression is a valuable stress marker in eco-physiological studies.