We studied the effectiveness of antithymocyte globulin (ATG) in preventing acute graft-versus-host disease (a-GVHD) in children who received bone marrow transplants from unrelated HLA-matched donors at one institution. Of 39 patients who received transplants between 1993 and 1997, 23 were given ATG on the basis of informed consent. Either Thymoglobulin (Pasteur Merieux, 2.5 mg/kg/day) or Lymphoglobulin (15 mg/kg/day) was administered for 4 days. a-GVHD (> or = grade II) developed in 33% of the ATG group (n = 21) and in 44% of the non-ATG group (n = 16). Although a-GVHD (> or = grade II) appeared less frequent in the ATG group, the difference was not statistically significant. Among the subjects with hematological malignancies, no significant difference was observed in frequency of a-GVHD (> or = grade II) or 3-year survival rate for the ATG group (n = 10) and non-ATG group (n = 16). However, the incidence of cytomegalovirus infection was much higher (p < 0.01) in the ATG group (70%) than in the non-ATG group (19%). From this study, we were not able to confirm the benefits of ATG as described by other investigators.