Angiotensin II (ANG II) can have multiple effects on the kidney, including influences on the regulation of glomerular hemodynamics and tubular transport as well as consequences for the glomerular processing of macromolecules. The recognized suppressive effects of angiotensin-converting enzyme inhibitors on compensatory renal growth, even in the absence of hemodynamic effects, and the well-documented proliferative effect of ANG II on vascular smooth muscle cells have provided the background for the recent intensive interest in this peptide as a renal cytokine. Diverse cell types along the nephron express a variety of ANG II receptors. These receptors and their putative signal transduction pathways have been best characterized in mesangial and proximal tubular cells. Culture experiments provide convincing evidence that ANG II can be a phenotypic influence on these cell types. The growth responses and the associated signal transduction pathways, however, are different in mesangial and proximal tubular cells. These ANG II-mediated responses are also associated with an increase in the synthesis of distinct collagen subtypes, potentially linking the growth stimulatory effects of ANG II to the irreversible changes of glomerulosclerosis and tubulointerstitial fibrosis observed in chronic renal failure. Preventing the intrarenal actions of ANG II with angiotensin-converting enzyme inhibitors or with the new, orally active, selective ANG II receptor antagonists may provide a rational therapeutic approach to attenuate the progression of a variety of kidney diseases.