Several cord blood banks store cord blood units from healthy siblings of patients, who are candidates for stem cell transplantation. We analyzed the quality characteristics of 50 cord blood units collected from families with beta-thalassemia major and the outcome of subsequent stem cell transplantations during a 15-year period. All cord blood units were found suitable for banking based on a minimum net volume of 40 ml. The mean volume of the units was 98.9 ml; the mean total nucleated cell count (NC) was 7.8 x 10(8) and the mean CD34+ cell count was 2.8 x 10(6). Eight out of twelve HLA matched collections were released for transplantation. All but one recipient belonged to Pesaro II-III risk classes. Three patients received a cord blood graft with >5 x 10(7) NC/kg . One of them with Pesaro class I disease engrafted, whereas the other two who failed to engraft, were re-transplanted with bone marrow from the same donor later. Cord blood grafts containing NCs <4 x 10(7)/kg combined with reduced volume bone marrow from the same donor were used in all 5 remaining cases and stable engraftment was achieved. All patients survived, 7/8 thalassemia-free. Cord blood banking from healthy siblings of children with beta-thalassemia major can result in a successful transplantation in cases in which there is HLA compatibility. However, in high-risk patients, the use of combined cord blood and bone marrow grafts seems necessary in order to ensure stable engraftment, especially when cord blood unit cell counts are low.