Vascular endothelial growth factor (VEGF) is known to play an essential role in vascular development. We have overexpressed VEGF(122) or VEGF(170), which are equivalent to mouse VEGF(120) and VEGF(164), in developing Xenopus embryos. Overexpression of VEGF(170) but not VEGF(122) demonstrated an absence of expression of hematopoietic markers alpha-globin and GATA-1 but only in the posterior portion of the blood island. Interestingly, strong signals of endothelial markers, msr, fli-1, and tie-2, were detectable in those regions, instead of hematopoietic markers. These results suggested both that injection of VEGF(170) resulted in disturbance of vasculogenesis in the posterior portion of the blood island, with excessive production of endothelial cells at the expense of blood cells, and that the anterior and posterior portions of the VBI may have distinct characteristics. (c) 2006 Elsevier Inc. All rights reserved.