Excessive cellular growth is a major contributor to pathological changes associated with diabetic nephropathy. In particular, high glucose-induced growth of glomerular mesangial cells is a characteristic feature of diabetes-induced renal complications. Glomerular mesangial cells respond to traditional growth factors, although in diabetes this occurs in the context of an environment enriched in both circulating vasoactive mediators and high glucose. For example, the vasoactive peptide ANG II has been implicated in the pathogenesis of diabetic renal disease, and recent findings suggest that high glucose and ANG II activate intracellular signaling processes, including the polyol pathway and generation of reactive oxygen species. These pathways activate the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) signaling cascades in glomerular mesangial cells. Activation of the JAK/STAT signaling cascade can stimulate excessive proliferation and growth of glomerular mesangial cells, contributing to diabetic nephropathy. This review focuses on some of the key elements in the diabetic microenvironment, especially high glucose and the accumulation of advanced glycoxidation end products and considers their impact on ANG II and other vasoactive peptidemediated signaling events in vitro and in vivo. ANG II; high glucose; glomerular mesangial cells; advanced glycoxidation end products GLOMERULAR MESANGIAL CELLS possess both contractile and mitogenic properties and contribute to the physiological regulation of glomerular dynamics (30,73). Growth factors have a maladaptive role in the glomerular damage accompanying experimental and human glomerulonephritis. This is especially evident in diabetic nephropathy through enlargement of the glomerular remnant and mesangial matrix expansion associated with the accumulation of extracellular matrix proteins synthesized by glomerular mesangial cells (12,30,73). The vasoactive peptide ANG II, not usually considered in the context of traditional growth factors, has been implicated in both normal and diabetic cellular growth (3, 64). Our group has found that activation of the Janus kinase (JAK)/signal transducers and activation of transcription (STAT) pathway is essential for ANG II-induced growth of glomerular mesangial cells (4,70). In addition, we have recently shown that high glucose augments ANG II-induced activation of the JAK/STAT pathway in rat kidney glomeruli (7) and that this pathway contributes importantly to production of the cytokine TGF- as well as the extracellular matrix proteins collagen IV and fibronectin (70). Furthermore, recent studies also demonstrate that high glucose induces intracellular production of reactive oxygen species (ROS) (24), which have been shown to augment ANG II-induced signaling cascades and to activate JAK and STAT proteins (63,68).Renal disease is one of the leading causes of morbidity and mortality in patients with diabetes mellitus, and ANG II has been implicated in the pathogenesis of maladaptive growth in renal tissues...