The aim of this study was to investigate gamma radiation--induced oxidative damage in erythrocytes after dynamic renal scintigraphy with 370 MBq Tc-99m diethylene trimine pentaaceticacid (DTPA) and bone scintigraphy with 740 MBq Tc-99m methylene diphosphonate (MDP). Thirty patients who performed dynamic renal scintigraphy (15 patients) and bone scintigraphy (15 patients) were included in this study. The median ages were 507 years (range, 21-69 years) and 558 years (range, 34-78 years) for dynamic renal scintigraphy and bone scintigraphy, respectively. The blood samples were taken from patients just before, 1h after, and 3h after injection of the radiopharmaceutical. Malondialdehyde (MDA) and antioxidant enzymes such as glutathione peroxidase (GPX), superoxide dismutase (SOD), and catalase (CAT) levels were measured to evaluate the gamma radiation--induced oxidative damage. The enzyme activities of CAT were decreased 1 and 3h after injection of the radiopharmaceutical in both groups (p0.05). In both groups, the enzyme activities of SOD and GPx were decreased 1 and 3h after injection of the radiopharmaceutical, respectively. MDA levels were increased 3h after (p0.05) injection of the radiopharmaceutical in both groups.