Ongoing investigation into the relationship between the renin-angiotensin system (RAS) and the progression of diabetic renal disease has persisted for the past two decades. Experimental and clinical evidence suggests that the RAS has a pathogenic role, induced by its haemodynamic and non-haemodynamic mechanisms. The discovery of a local intrarenal RAS provides a rationale for investigating the components of RAS, specifically Angiotensin II (AngII) in the diabetic setting. AngII has multiple effects, including activating intracellular second messengers, transcription factors, extracellular matrix protein and also growth factors and cytokines, which lead to many of the structural and functional changes in the diabetic kidney. The beneficial effects afforded by RAS blockade further implicate AngII in the progression of diabetic nephropathy. Although AngII is a common suspect in the pathogenesis of diabetic nephropathy RAS blockade does not prevent patients from progressing to end stage renal disease. Evaluating other vasoactive factors, which have similar and distinct functions to AngII, will assist in understanding their potential role in the pathogenesis of diabetic nephropathy. A large number of researchers are studying vasoactive factors, however, the case for their role in diabetic nephropathy is inconclusive. Further investigation into the effects of inhibiting vasoactive compounds, including endothelin, urotensin II and vasopeptidases, together with inhibiting RAS, may provide another therapeutic avenue for treating diabetic nephropathy.