The effect of 0.3 μg TPO 24 hours or 2 hours after TBI on the regeneration of bone marrow progenitors after 6 Gy TBI in mice. GM, GM-CFU; E, BFU-E; and Meg, CFU-Meg per femur at day 7 after TBI (means ± SE). The open bar (□) represents control mice (n = 6), the lightly shaded bar (▧) represents mice treated with TPO 24 hours after TBI (n = 6), and the dark shaded bar (▧) represents mice treated with TPO 2 hours after TBI (n = 6). *Significant compared with control mice (P < .03),^#significant compared with mice treated with TPO 24 hours after irradiation (P < .03).