ROS levels modulated the temporal kinetics of femoral hematopoietic reconstitution. C57BL/6 recipient mice (10 mice in each group) were orally treated with NAC 8 hours before irradiation, at the time of irradiation, and 24 or 48 hours after irradiation until 1 month after transplantation. At 24 hours after irradiation at 10 Gy, C57BL/6 recipient mice were transplanted with 1000 LSKCD34− GFP+ hematopoietic cells. Pictures in panels A and B represent selected frames (knee, diaphysis, and femoral head areas) of 30 seconds to 50 seconds acquired videos (scale bar represents 50 μm) obtained 9 (A) or 13 and 15 (B) days after transplantation for each mouse group. (A) Only transplanted mice treated with NAC 24 hours and 48 hours after irradiation displayed the same density of GFP+ hematopoietic cells as untreated transplanted mice. (B) The delay in the cellular density of GFP+ hematopoietic cells of mice treated with NAC at the time of irradiation was diminished 13 days after transplantation and was recovered 15 days after transplantation. (C top panel) Relative fluorescence units of individual cells detected in all frames of the femoral head 1, 2, 3, 5, and 7 days after transplantation of 1000 CFSE-labeled LSKCD34− cells into mice not treated or treated with NAC at the time of irradiation or 24 hours after irradiation was quantified. One, 2, 3, 5, and 7 days after transplantation, videos of the hematopoietic reconstitution were recorded in the 2 femurs of 3 different mice. Pictures acquired from videos of the femoral head show one of the few frames that contain single CFSE-labeled cells. White and blue arrows, respectively, indicate cells with fluorescence intensities more than 100 or approximately 80. **P < .05; ***P < .001. (Bottom panel) Graphics show the distribution of relative fluorescence units of each cell present in the analyzed frames and the means of these individual relative fluorescence units. These values, together with the cell number detected and the mean fluorescence above background (which is 60, as shown in Figure 1B), are shown below graphics. The data are representative of those obtained in 3 different mice. Statistical analysis was performed with the 1-way analysis of variance test.