GFP-positive muscle fibers are from stem-cell populations of marrow cells. Different populations of marrow cells were infused into C57BL/6 mice after 500 cGy whole-body and 500 cGy lower-extremity radiation. Animals received cardiotoxin injury to their right tibialis anterior muscle 1 week after transplantation, and their muscles were analyzed for the presence of GFP-positive muscle fibers. The numbers of cells injected for whole bone marrow (WBM) were 3 × 10⁶ cells; CD45^- and CD45⁺, 2 × 10⁶ cells; Lineage^- and Lineage⁺, 1.4 × 10⁶ cells; c-Kit⁺ and c-Kit^-, 2.16 × 10⁶ cells; and Sca-1⁺ and Sca-1^-, 8 × 10⁵ cells each. Data represent average ± SE from 3 to 6 animals in each group. All the differences between the positive and negative groups in each population were statistically significant (P < .05). Error bars indicate mean ± standard error.