The efficacy of methotrexate (MTX) as a single graft-versus-host disease (GVHD) prophylaxis agent was compared to that of cyclosporin A (CSA) in 62 pediatric patients (median age: 8 years) with hematological malignancies who had undergone bone marrow transplantation (BMT) from HLA-identical sibling donors at National Kyushu Cancer Center since 1977. In all, 30 patients received MTX by intravenous bolus injection, with a dose of 15 mg/m(2) on day +1, followed by 10 mg/m(2) on days +3, +6, and +11, and then once a week until day +100. A total of 32 patients were treated with CSA, which was given intravenously in the early stages and orally thereafter until day +100, and then gradually tapered and stopped 6 months after BMT. There were no differences between the groups in terms of rates of hematopoietic recovery after BMT. The probabilities of acute GVHD (grades II-IV) and chronic GVHD were 29.6 vs 40.6% (P=0.294) and 19 vs 20% (MTX vs CSA), respectively. Relapse rates and event-free survival were identical. These results suggest that MTX and CSA were equally effective when given after BMT in Japanese pediatric patients with hematological malignancies. Since MTX was given over a shorter time than CSA, it might be more practical in the management of such patients.