In an attempt to reduce the complications associated with allogeneic bone marrow transplantation (BMT), a number of investigators in Europe, Australia, and the United States have evaluated umbilical cord and placental blood as a source of hematopoietic stem cells for transplantation. On the basis of prior laboratory investigations, cryopreserved umbilical cord blood stem cells (CBSC) were used in the treatment of 15 patients with malignant (n = 8) and nonmalignant (n = 7) disorders. The median recipient age was 4 years (range: 2-11 years). Thirteen donor-recipient pairs were HLA-identical and two were HLA-mismatched. While eight donor-recipient pairs were ABO-incompatible (6 major/2 minor), none of these 8 cord blood grafts was erythrocyte or plasma depleted prior to cryopreservation. After treatment with myeloablative doses of chem(radio)therapy, 14 of 15 patients received graft-versus-host disease prophylaxis consisting of cyclosporin A alone or in combination with other immunosuppressive agents. The mean volume of umbilical cord blood collected was 126.4 ml (range: 64-282 ml); the mean number of nucleated cells in the graft was 1.39 x 10(9). Hematopoietic recovery occurred in 13 of 15 patients with a median time to ANC > or = 500/microliters of 28.5 days. Mild cutaneous acute graft-versus-host disease was diagnosed in 5 of 11 evaluable patients with HLA-identical donors and in 1 evaluable patient with an HLA-mismatched donor; no patient had significant disease by report. The median follow-up of the 9 event-free survivors is 1.9 years (range: 0.3-4.2 years).(ABSTRACT TRUNCATED AT 250 WORDS)