Host-derived KGF is required for thymic reconstitution after syngeneic and allogeneic BMT. Lethally irradiated (1100 cGy) KGF^-/- or KGF^+/- mice were transplanted with B6.129-WT bone marrow (A-C) or BALB/c BM (D-F). Lethally irradiated (1100 cGy) B6.129 (G-H) or (900 cGy) BALB/c mice (J-L) were transplanted with KGF^-/- or KGF^+/- BM and were killed at day 28. Thymic and splenic cellularity was determined, and splenic CD3⁺, CD4⁺, and CD8⁺ T-cell numbers were calculated by flow cytometric analysis. Anti-H2^d antibody was used to determine the chimerism in allogeneic experiments. Values represent mean (± SEM) and n = 5-11 per group. ^*P < .05.