Between January 1993 and June 1994, the JMDP facilitated marrow donations from unrelated donors for 171 patients with malignant and non-malignant disorders. The median age of the patients was 21 years. All patients received marrow from phenotypically HLA -A, -B, -DR identical donors. About half of the patients wrer treated with total body irradiation (TBI)-containing regimens and about 80% of the patients received short-courses methotrexate and cyclosporine for graft-versus-host disease (GVHD) prophylaxis. Eight out of 171 patients, (4.7%) had graft failure and 63 out of 144 patients (44%), who survived for more than 30 days posttransplant, developed grade II to IV acute GVHD. The incidence of chronic GVHD was 47% (extensive form; 27%); most of them were progressive/quiscent type. The incidence of moderate to severe acute GVHD was higher than that observed in sibling transplants. On the other hand, the incidence of chronic GVHD was similar to that observed in sibling transplants. Overall survival at 1.5 years posttransplant was about 50% with no significant differences between diseases. The age correlated significantly with the survival in standard risk leukemia but not in high-risk leukemia. Despite the risk of graft failure and acute GVHD, this preliminary analysis demonstrates that transplantation of marrow from unrelated donors can be an effective treatment for certain hematologic disorders.