OBJECTIVE: We evaluated the potential detrimental cytogenetic effects of Tc-methoxyisobutyl isonitrile (MIBI) and I on patients who were exposed to the radiopharmaceutics for cardiac imaging or thyroid cancer therapy, respectively. METHODS: Mononuclear leukocytes were isolated both before and after radiopharmaceutical administration and subsequently cultured. Micronuclei frequency was then assessed and microscopic evaluation of apoptosis was conducted. RESULTS: Small statistically insignificant augmentation in the percentage of micronuclei from 10.9±3.8 to 11.3±2.4% was observed in the Tc-MIBI group. In contrast, I elicited a notable augmentation of micronuclei from 6.3±2.2 to 9.6±3.1 at 3.7 GBq, and 6±1.5 to 9.2±2.7 at 5.55 GBq (P<0.05). CONCLUSION: Our results showed that there were no remarkable alterations either in the micronuclei incidence or in the percentage of apoptotic lymphocytes after in-vivo exposure to radiopharmaceutical imaging, which provides evidence to reduce the growing concern about the safety issue of cardiac imaging with Tc-MIBI, whereas the deleterious effects of I must be considered when it is applied to thyroid cancer treatment.