Thymus-dependent reconstitution of the peripheral T-cell compartment is critical for the successful outcome of bone marrow transplantation. However, graft-versus-host disease (GVHD) affects thymic stromal function and thus prevents normal T-cell maturation and selection. To determine whether cytoprotection of thymic epithelial cells (TECs) by keratinocyte growth factor (KGF) averts GVHD-related injury to the thymus, a nonirradiated murine parent→F₁ transplantation model was investigated. Administration of KGF between days −3 and +3 of GVHD induction preserved normal thymic size, cellularity, and thymocyte phenotype when measured 2 weeks after transplantation and compared with saline-treated parent→F₁ mice that received allogeneic transplants. Moreover, the characteristic GVHD-induced impairment in cell cycle progression of pro- and pre-T cells was prevented by KGF. However, the normal phenotypic and functional status of the thymus did not correlate with the higher number of GVHD-inducing mature donor T cells in thymi of KGF-treated mice. Importantly, extensive analysis of the different TEC populations within the thymic cortex and medulla revealed an almost normal stromal architecture and composition in GVHD mice treated with KGF. These observations are likely to reflect an indirect effect of KGF on thymopoiesis as KGF-receptor expression was demonstrated to be restricted to TECs. Thus, pharmacologic doses of KGF appear to exert a potent effect on TEC function, which in turn allows for normal T lymphopoiesis to occur during acute GVHD.