We have injected human CD34+lin- cells derived from cord blood (CB) into the goat fetuses via in utero at 45-55 days gestation under guidance of B-scan ultrasonograph. Sixty out of 68 fetuses injected survived to full term. The long-term survival of the human cells in transplant goat has been tested by various experimental methods, including FACS analysis, real-time PCR, RT-PCR, Southern-blot hybridization, FISH, as well as immunohistochemical assays. All the 60 transplant goats demonstrated engrafted human cells, including myeloid, B-lymphoid, and erythroid lineages. The yield of the human CD34+ cells varied, but was not linked with sex and age. High numbers of human cells could be detected for at least 16 months after birth. Immunohistochemical analyses revealed that the human cells were present not only in blood but also in other tissues, such as liver, of the transplant goats. In addition, a human-specific serum albumin and the hepatocyte nuclear factor (hHNF-3beta) mRNAs specific to human hepato-antigen could be readily detected in the livers of the transplant goats. Our results demonstrate that this in utero xenograft model should be useful for expansion of human HSC and possibly for the evaluating the effectiveness of prenatal treatment of human genetic diseases.