To assess the extent of genetic damage in PBMC obtained from individuals repeatedly (whole body) exposed in vivo to MRI at 7T MRI scanners with field strengths of up to 3T are currently used for clinical purposes. Apart from comprehensive reviews¹, there have been some investigations examining the extent of genetic damage in human PBMC collected from individuals exposed to MRI. These studies were critically reviewed ² and few others were published more recently ^3-5.However the MRI exposure in these studies was at field strengths of up to 3T,single and of short duration. The current investigation had two objectives. (1) Evaluation of genetic damage in PBMC obtained from healthy individuals working with and around UHF 7T MRI scanners as well as healthy volunteers who participate frequently in 7T MRI research investigations. These individuals were repeatedly exposed to 7T MRI. The observations were compared with those in healthy individuals who were not exposed to MRI and in positive control cells exposed to 0.2 Gy γ-radiation. (2) Lymphocytes from these individuals were additionally exposed in vitro to 7T MRI for 1 hour in order to determine any further impact of in vitro exposure on genetic damage.Twenty two healthy male individuals, non-smoking, non-alcoholics, between the ages of 22 and 54 years participated in the study. The damage in PBMC was assessed using anti-γH2AX immunofluorescence staining of DNA double-strand breaks (DSB) in un-stimulated cells at 1, 20 and 72 hours post-exposure and by quantification of micronuclei (MN) in activated cells. For the additional in vitro exposures, the Echo Planar Imaging pulse sequence with an 8-channel head coil was used in normal operating mode for 1 hour. The sequences utilized an average RF power of 50 W, a maximum gradient strength of 65.43 mT/m and a maximum slew rate of 186 mT/m/ms. The TR and flip angle were adjusted to reach the maximum permissible SAR level for the head.The results obtained for DSB (γ-H2AX foci/cell) and MN in REP and CTL cells as well as in positive controls expose to 0.2 Gy γ -radiation are presented in Fig.1 and Fig.2. Our results did not indicate significant differences in the baseline γH2AX foci and MN between individuals repeatedly exposed to 7 T MRI and un-exposed individuals. The results from in vitro exposure of cells to 7 T MRI did not have additional impact: In contrast, positive control cells exposed to 0.2 Gy g-radiation showed significant increase in DSB and MN.The results in our investigation indicated that repeated 7T MRI exposure was not able to induce excess genetic damage. Such exposure can be considered safe. However, further large-scale investigations examining biological consequences using potentially more sensitive biomarkers may be needed to transfer UHF MRI into a widespread diagnostic tool and address concerns raised in previous publications.