Between February 1988 and January 1990, 35 patients underwent allogeneic bone marrow transplantation (BMT) from unrelated donors using measures routinely employed for matched related donors. Median patient age was 34 years (range 2-49). Thirty-two patients had hematologic malignancies, including chronic myelogenous leukemia (CML) in 16; three patients had severe aplastic anemia. Donor-patient pairs were matched at the HLA loci tested serologically (HLA-A, -B, -DR) in 29 cases; mixed leukocyte culture results were variable but often reactive. Five patients died prior to day +28 without evidence of myeloid engraftment, and one patient developed fatal graft failure several months after initial engraftment. Acute graft-versus-host disease (GVHD) occurred in 77% (95% confidence interval [CI] 60-90%) of all patients, and GVHD contributed to the death of 10 patients. Fatal regimen-related toxicity occurred in four patients and another died due to neurologic complications of a process that resembled the hemolytic-uremic syndrome. Two acute leukemia patients relapsed, and a CML patient was found to have a localized non-Hodgkin's lymphoma at necropsy. As of 1 June 1991, 14 patients are alive and in remission at a median follow-up of 1.9 years (range 1.5-3.3); all except one have normal performance scores. The 2-year actuarial event-free survival for all patients is 40% (95% CI 24-56%). Proportional hazards analysis revealed favorable significance for female patient sex, less advanced disease status and shorter interval from diagnosis to BMT. While unrelated-donor transplants need not necessarily duplicate the results of related-donor transplants to be of benefit, the event-free survival in this series was roughly similar to that expected in the related-donor situation, with the high transplant-related mortality somewhat offset by a low recurrence rate. Further studies using unrelated donors, employing new methods of preventing transplant-related complications, are indicated.