Irradiation conditioning of the thymus reduces homing of progenitors. (A) Short-term homing assay was performed with unconditioned recipients or recipients receiving 900 cGy irradiation to the upper (includes thymus) or lower half (excludes thymus). Cocultures were analyzed by flow cytometry between 2 and 3 weeks later (n = 3; P < .05 comparing upper half to unconditioned using Fisher’s exact test). (B) Short-term homing assay was performed on unirradiated recipients or recipients receiving 900 cGy directed irradiation of the thymus (DI). Cocultures were analyzed between 2 and 3 weeks later (n = 3; P < .05 using Fisher’s exact test). (C) Short-term homing assay was performed on mice 2 weeks after mice were left unirradiated or irradiated with 900 cGy of directed thymic irradiation. Cocultures were analyzed between 2 and 3 weeks later (n = 2).