Vascular permeability factor (VPF)/vascular endothelial growth factor (VEGF) is a approximately 43-kDa secreted protein that has been shown in bioassays to induce endothelial proliferation, angiogenesis, and capillary hyperpermeability. VPF has been suggested to play an important role in the physiology of normal vasculature. To further elucidate the natural functions of VPF in vivo, the expression of VPF in normal tissues was examined using Northern blot analysis and in situ hybridization histochemistry. VPF mRNA is expressed in the brain, kidney, liver, lung, and spleen of the healthy adult rat. On Northern blots, the relative abundance of VPF mRNA observed in these tissues was highest in the lung and lowest in the spleen. As determined by in situ hybridization, the patterns of VPF expression are organ specific. Hybridization of an antisense VPF probe was concentrated in the cerebellar granule cell layer of the brain and in the glomeruli and tubules of the kidney. In the liver and lung, intense hybridization was observed homogeneously throughout both tissues, demonstrating that VPF mRNA is present in virtually every hepatocyte and pulmonary alveolar cell. Hybridization to the spleen was weaker and more diffuse. The widespread expression and organ-specific distribution of VPF mRNA in normal rat tissues supports the suggestion of an extensive role for this factor in the physiology of normal vasculature.