Vascular permeability factor (VPF), also known as vascular endothelial cell growth factor (VEGF), is a 34- to 43-kDa dimeric protein synthesized and secreted by a variety of tumor and normal cells. At nanomolar concentrations, VPF causes an increase in microvascular permeability and is thought to be responsible for enhanced permeability of tumor blood vessels and for the fluid accumulation associated with solid and ascites tumors. In addition, VPF/VEGF is a mitogen for endothelial cells and may play an important role in maintaining vascular endothelium and in promoting tumor angiogenesis. Antibodies were raised against a series of synthetic peptides derived from the predicted human VPF amino acid sequence. The antibodies were assayed for their ability to bind native and denatured/reduced VPF. Antibodies to peptides from the N- and C-termini bound both denatured/reduced and native VPF; antibodies directed to internal segments (e.g., amino acids 27-48 and 85-101) strongly bound denatured/reduced VPF but were substantially less effective at binding native VPF. These results suggest that the N- and C-termini are exposed regions of the protein in solution. Individually, antibodies to the N- and C-termini each partially blocked VPF permeability activity, and, in combination, blocked nearly 100% of this activity. Also, the N- and C-terminal antibodies blocked the VPF-mediated stimulation of both endothelial cell growth and increase in free cytosolic calcium.