Cadmium (Cd) is a non-redox metal that can indirectly cause oxidative stress by depleting cellular levels of glutathione. It is well-known for the generating reactive oxygen species (ROS) such as hydroxyl radicals, superoxide anions, nitric oxide, and hydrogen peroxide. The latter inactivates antioxidant enzymes and induces lipid peroxidation and DNA damage in cells. In our study, we have investigated the ameliorative effect of limonene against Cd-induced genotoxicity using various biomarkers such as sister chromatid exchange (SCE), comet, and lipid peroxidation (LPA) assays in cultured human peripheral blood lymphocytes (PBL) from healthy individuals. It is a naturally occurring flavonoid, found in essential oil of citrus fruits. Limonene at 20-mu M and 100-mu M concentrations had significantly (P < 0.05 and P < 0.01) reduced the SCE frequency, tail moment, and peroxidation of lipids. Ameliorative effect of limonene was also determined by measuring the activity of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT). We found a significant increase (P < 0.05) in the enzyme activity after limonene treatment. We also studied the effect of GSTP1 gene polymorphism on Cd-induced genotoxicity and antigenotoxic potential of limonene. We found a significant decrease (P < 0.05) in SCE frequency, tail moment, and lipid peroxidation after limonene treatment compared to Cd. However, we did not observe any significant relationship (P > 0.05) between GSTP1 polymorphism and Cd, limonene genotoxicity and antigenotoxicity, respectively.