The aim of this study was to investigate gamma radiation-induced oxidative damage in erythrocytes after Tl-201 myocardial perfusion scintigraphy. Twenty patients (8 women and 12 men) who performed Tl-201 myocardial perfusion scintigraphy were included in this study. The blood samples re taken from patients just before, I hour after and three hours 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 SOD, GPX and CAT were decreased I hour after (p = 0.042, p = 0.697 and p = 0.653 respectively) and 3 hours after (p = 0.003, p = 0.5 73 and p = 0.002 respectively) injection of the radiopharmaceutical. Malondialdehyde levels were increased I hour after (p = 0.10) and 3 hours after (p = 0.47) injection of the radiopharmaceutical. In this study, we found that radiation due to Tl-201 myocardial perfusion scintigraphy decreased the erythrocyte antioxidant levels and increased MDA levels.