The first cooperative study of the Asian Pacific bone marrow transplantation group included 75 patients with early leukemia who received human leukocyte antigen-matched sibling bone marrow transplants and were randomized into granulocyte colony-stimulating factor and control groups. The selected patients were registered from 10 centers in six countries and areas within Asia (Beijing, Taipei, Hong Kong, Japan, Korea, and Malaysia). The incidence of grades II-IV acute graft-vs.-host disease was 22.2%, and the 2-year survival rate was 62.7%. The period of protective isolation (27.1-66.7 days), period of hospitalization (38.6-130.5 days), and medical costs for 4 months (US $10,300-US $80,803) varied considerably. Good cooperation, i.e., low rate of protocol violation or rapid and precise presentation of case reports, was obtained.