(A) Overview of the essential steps of the modified and automated FADU assay. After preparation of the cells, DNA damage is inflicted, followed by further incubation to allow DNA repair. The automated steps are highlighted in bold. (B), (C) Dose-dependent induction of DNA strand breaks by X-rays in human PBMC (B, high dose range; C, low dose range). PBMC were exposed to various doses between 0 and 16.2 Gy. Note that the percentage of unwound DNA increased with increasing doses. Data are presented as means ± SDs from 3 independent experiments performed on PBMC from different donors. The detection threshold was set as mean minus 3 SD of the unirradiated controls (P0).