Thalassemic children are at a high risk of graft rejection in cord blood transplantation. To investigate this possible mechanism, the authors evaluated the effect of panel reactive antibody on the growth of CD34(+) cells in vitro. On semisolid medium, CD34(+) cells derived from cord blood were incubated with thalassemic serum, and colony-forming units were counted after 10 days of culture. After incubation with serum-specific panel reactive antibody, profound decreases were found in the numbers of CFU-GM, CFU-GEMM and BFU-E compared with controls. The results indicated that serum-specific panel reactive antibody might have an apparent inhibition effect on proliferation and differentiation of cord blood CD34(+) cells.