SUMMARY1. We characterized the endothelial cell‐derived growth factors of SHRSP and Wistar Kyoto rats (WKY), respectively and found that platelet‐derived growth factor (PDGF)‐B chain related growth factor constituted a major portion of the mitogenic activity of the conditioned media of endothelial cells from both animals. There were no remarkable qualitative differences between the endothelial cell‐derived growth factors of SHRSP and WKY.2. Northern analysis revealed that the expression of PDGF‐B chain was 2–4‐fold enhanced in cultured aortic endothelial cells of SHRSP. This enhanced expression of PDGF‐B chain, which may be induced under chronic hypertensive conditions, is suggested to contribute to the increase in endothelial cell‐derived growth factors report