RESUMEN
<p><b>OBJECTIVE</b>To study the expression and distribution of KDR, VEGF and CD34 in yolk sac and liver of human embryo at different development stage.</p><p><b>METHODS</b>Yolk sacs and livers of 15 human embryos were analyzed by the immunohistochemical SP kits for the expression of KDR, VEGF and CD34.</p><p><b>RESULTS</b>KDR, VEGF and CD34 were all expressed in yolk sacs and livers of the embryos. In the intermediate liver group, the grey value of KDR and VEGF were 103.8 +/- 6.1 and 96.4 +/- 6.3, respectively, stronger than that in the late liver group which were 90.4 +/- 6.0 and 87.4 +/- 6.3, respectively (P < 0.05). A positive correlation between the levels of KDR and VEGF was observed (P < 0.05).</p><p><b>CONCLUSION</b>The expression of KDR and CD34 in yolk sac and liver of embryo suggests the presence of hemangioblast in these organs. Interaction of KDR and VEGF might relate to survival, proliferation, migration and differentiation of hemangioblasts.</p>