Summary:Some cytokines are believed to play a role in the development of acute and chronic GVHD after allo-hematopoietic stem cell transplantation. It has been reported that TNF-␣ and IL-10 gene polymorphisms are associated with the production of those cytokines and the development of graft failure after organ transplantation and systemic lupus erythematosus. We examined whether TNF-␣ and IL-10 gene polymorphisms affect the severity of acute GVHD (aGVHD) and chronic GVHD (cGVHD). Sixty-two and 54 patients were available for the analysis of aGVHD and cGVHD, respectively. We analyzed the gene polymorphisms derived from preand post-transplant blood cells. Donor-derived TNF2 allele (A) was more frequently detected in patients with aGVHD III/IV than those aGVHD 0-II (2/6 vs 2/56) (P ؍ 0.04). The donors of the patients with cGVHD more frequently possessed a greater number of alleles (allele 13 or more which contain 26 or more CA repeats) in IL-10·G than those without (13/26 vs 5/28) (P ؍ 0.02), and the patients with cGVHD had more CA repeats in donor-derived IL-10·G than those without (mean ؍ 25.2 vs 23.4) (P ؍ 0.01). Donor-derived TNF-308 and IL-10·G alleles may contribute to severe aGVHD and cGVHD, respectively, and will help us distinguish those patients at high risk for GVHD. Bone Marrow Transplantation (2000) 26, 1317-1323.