Radiation is not essential for marrow-to-muscle conversion. Male NOD/SCID mice received transplants of 12 million GFP lineage-negative, GFP-positive marrow cells from transgenic mice after different doses of lower-extremity and/or whole-body radiation. One week later, anterior tibialis muscles were injured with injection of cardiotoxin directly into the muscle. Analyses were performed 1 month after injury by calculating the percentage of GFP-positive fibers to the total number of fibers. Charts represent the average for peripheral blood chimerism of GFP-positive cells, weight of right tibialis anterior muscle, the percentage of muscle GFP-positive fibers, and the percentage of muscle GFP-positive fibers corrected for their weight, in each group. In this model of regeneration, at higher doses of local or systemic radiation, peripheral blood and muscle chimerism increases but the muscle weight decreases. Three mice in each group were evaluated. Error bars indicate mean ± standard error.