Background Allogeneic hematopoietic stem cell transplantation (HSCT) is the preferred treatment for a number of life-threatening diseases, including acute leukemia and aplastic anemia. However, HSCT is frequently complicated by syndromes characterized by endothelial dysfunction, such as graft-versus-host disease (GVHD) or veno-occlusive disease. The transforming growth factor beta (TGF-beta) superfamily protein activin A is required for endothelial integrity and tissue repair. TGF is a tumor suppressor that induces apoptosis or autophagy, inhibits the cell cycle, and regulates cytokine and chemokine expression. Many mutations in genes encoding receptors and decreased expression of TGF pathway components have been observed in carcinoma. Activin A has been shown to play dual roles in cancer progression, depending on genetic and cellular context as well as tumor stage, exerting early tumor-suppressive and late prometastatic effects. Aims The goal of this study was to measure activin A levels before and after allogeneic HSCT and to correlate serum activin A with posttransplantation GVHD. Patients and methods Serum activin A was measured using an enzyme-linked immunosorbent assay in 30 preallogenic bone marrow transplant patients in comparison with 10 healthy controls recruited from the bone marrow transplantation unit at Ain Shams University Hospitals. Result The serum activin A level was higher in allogenic transplantation patients than in controls, with a statistically significant difference between patients and controls (P=0.001). Activin A was found to be associated with chronic GVHD (P=0.004 and 0.002, respectively). Conclusion Activin A levels are useful biomarkers for detecting GVHD from allogeneic bone marrow transplantation.