We herein examined the biological effects of cells treated with F-18 labeled drugs for positron emission tomography (PET). The relationship between the intracellular distribution of F-18 and levels of damaged DNA has yet to be clarified in detail. We used culture cells (Chinese Hamster Ovary cells) treated with two types of F-18 labeled drugs, fluorodeoxyglucose (FDG) and fluorine ion (HF). FOG efficiently accumulated in cells, whereas HF did not. To examine the induction of DNA double strand breaks (DSB), we measured the number of foci for 53BP1 that formed at the site of DNA DSB. The results revealed that although radioactivity levels were the same, the induction of 53BP1 foci was stronger in cells treated with F-18-FDG than in those treated with F-18-HF. The clonogenic survival of cells was significantly lower with F-18-FDG than with F-18-HF. We concluded that the efficient accumulation of F-18 in cells led to stronger biological effects due to more severe cellular lethality via the induction of DNA DSB. (C) 2014 Elsevier Inc. All rights reserved.