To understand the role of vascular endothelial growth factor (VEGF) in placental development, we examined immunohistochemically 56 placentae ranging from 6--41-weeks gestation using rabbit antibody to a synthetic multiple antigen peptide (MAP), composed of N-terminal amino acid residues 1--20 of human VEGF. In the present study, syncytiotrophoblast and invading extravillous trophoblasts ubiquitously expressed VEGF throughout gestation. However, the expression of VEGF in syncytiotrophoblasts was uneven in the first trimester and most intense at the sprouting sites. In addition, some stromal cells in the villi and decidual cells were also positive in the first trimester. A morphometrical analysis of the ratio of the VEGF-positive cell area to the capillary area in the terminal villi statistically revealed a critical point of change at 16 weeks' gestation. These results provide further evidence to support the hypothesis that VEGF, locally expressed by trophoblasts, stromal cells in villi and decidual cells, may play an important role in the physiological growth and function of the vascular system in the villous stroma and basal plate during placental development and maturation.