In HLA-identical sibling bone marrow transplantation, certain recipient cytokine gene polymorphism genotypes and minor histocompatibility differences influence the occurrence and severity of acute graft-versus-host disease (aGvHD). The present study investigated the role of cytokine tumor necrosis factor (TNF)-alpha and interleukin (IL)-10 gene polymorphisms HY, HA-1, and CD31 minor histocompatibility antigen (mHag) mismatch in the development of aGvHD after unrelated cord blood (CB) transplant (CBT). DNA samples of 115 CB recipients and their unrelated CB grafts were analyzed for genotype associated with TNF-alpha (TNFd3/d3) and IL-10 (IL-10(-1064), 11-16) and for disparities in major and three minor histocompatibility antigens, HY, HA-1, and CD31 codon 125. Results were correlated with the incidence of aGvHD grades II to IV. Neither the donor nor the recipient GvHD risk alleles TNFd3/d3 and IL-10(-1064) (11-16) were associated with the development of aGvHD grades II to IV and I to IV. Because of the heterogeneity of CBTs, the data were reanalyzed separately for patients with malignancies (n=83) or with inborn errors (n=24). No significant association was observed between the severity of aGvHD and the possession of either TNFd3/d3 or IL-10 (11-16) genotypes. Mismatches for the mHags HY, HA-1, and CD31 exon 125 between donor and recipient did not associate with aGvHD grades II to IV. In contrast to HLA-identical sibling bone marrow transplantation, in mismatched unrelated CBT, neither the cytokine genotypes TNFd3/d3 alone or in combination with IL-10(-1064) alleles nor the minor histocompatibility antigens HY, HA-1, and CD31 exon 125 were associated with aGvHD grades II to IV. Further determination of the cytokine gene polymorphism genotypes in CBTs compared with bone marrow transplants may identify those polymorphisms that could be potential predictive markers for the occurrence of aGvHD.