Vascular permeability factor (VPF), also known as vascular endothelial growth factor (VEGF), increases microvascular permeability and is a specific mitogen for endothelial cells. Expression of VPF/VEGF previously was demonstrated in a variety of tumor cells, in cultures of pituitary-derived cells, and in corpus luteum. Here we present evidence, by Northern analysis and in situ hybridization, that the VPF/VEGF gene is expressed in many adult organs, including lung, kidney, adrenal gland, heart, liver, and stomach mucosa, as well as in elicited peritoneal macrophages. The highest levels of VPF/VEGF transcripts were found in epithelial cells of lung alveoli, renal glomeruli and adrenal cortex, and in cardiac myocytes. The prominence of VPF/VEGF mRNA in these tissues suggests a possible role for VPF/VEGF in regulating baseline microvascular permeability, which is essential for tissue nutrition and waste removal. We also demonstrate particularly high VPF/VEGF mRNA levels in several human tumors, where it may be involved in promoting tumor angiogenesis and stroma generation, both as an endothelial cell mitogen and indirectly by its permeability enhancing effect that leads to the deposition of a provisional fibrin gel matrix.