Interruption of the renin-angiotensin-aldosterone system (RAAS) by converting enzyme inhibition or angiotensin II (ANG II) receptor antagonism dramatically reduces injury in the remnant kidney model. Furthermore, converting enzyme inhibition reduces proteinuria and slows the decline in renal function in clinical disease. Hemodynamic actions of ANG II in the kidney in conjunction with a more poorly defined effect of the RAAS on systemic hypertension have been posited as the major mechanisms for maintenance of elevated glomerular pressure. Reductions in glomerular pressure have been attributed, at least in part, to removal of intrarenal effects of ANG II. Growth and fibrotic actions of ANG II may also contribute to progressive renal injury and relief from them reduce injury. The participation of circulating aldosterone in the remnant kidney model has been recently raised. Hyperaldosteronism and adrenal hypertrophy attend the hypertension, proteinuria, and glomerulosclerosis of this model. Although the hemodynamic actions of aldosterone probably account for some of the adverse effects it has in this model, other direct cellular actions may participate in its renal, as well as cardiac and fibrotic consequences. Thus, the RAAS, working through both ANG II and aldosterone, contributes to chronic progressive renal injury.