Groups of 20 Gy thoracic irradiated C3H/HeNHsd and C57BL/6NHsd mice were injected intraperitoneally (I.P.) with 1 × 106 syngeneic luc+ bone marrow stromal cells at each of four time points: 1) immediately, 2) at 67 days, 3) 129 days, or 4) 134 days post thoracic irradiation according to published methods (28, 30). In vivo imaging revealed no detectable migration of luc+ cells to the lungs of 20 Gy thoracic irradiated C3H/HeNHsd mice at any time point: A) acute phase; B) the latent period; or C) the late phase. In contrast, C57BL/6NHsd mice revealed significant late phase migration of luc+ BM cells to the lungs at day 129, D). Late phase bioluminescence in C3H/HeNHsd mice was compared to late phase bioluminescence in C57BL/6NHsd mouse lungs using a two-sided two-sample t-test. Pulmonary migration of luc+ cells was significantly increased (p<0.05) in C57BL/6NHsd compared C3H/HeNHsd mouse lungs (Fig. 3D).