Neutrophil chemotactic and functional defects occur in beta-thalassemia and in patients after bone marrow transplantation (BMT). Interleukin-8 (IL-8) is a novel chemotactic and activating peptide for neutrophils and can be detected in the circulation. IL-8 serum concentrations were evaluated in 30 beta-thalassemic patients before and after BMT. Serial samples from 16 patients were also studied. Fourteen sera from healthy children, 43 patients with chronic viral hepatitis, 16 patients on chronic transfusion treatment for various hematologic disorders, and 28 healthy adults were studied as controls. IL-8 was evaluated by an enzyme-linked immunosorbent assay. Patients with beta-thalassemia had higher IL-8 concentrations than did normal controls, patients with liver disease, and patients on chronic transfusion. beta-Thalassemic patients with severe liver siderosis and fibrosis had the highest IL-8 concentrations. After BMT in patients with successful engraftment, IL-8 concentrations decreased significantly. In contrast, in patients with acute graft-versus-host disease (GVHD), IL-8 concentrations were not statistically different from the concentrations found before BMT and were higher than in patients with no complications and patients with graft rejection. IL-8 may play a part in the immune dysregulation that occurs in beta-thalassemia and may be involved in the immune mechanisms leading to GVHD.