Background and objectives: Addition of aldosterone antagonists (AA) might provide renal benefits to proteinuric chronic kidney disease (CKD) patients over and above the inhibition of renin-angiotensin system blockers (RAS). We evaluated the benefits and harms of adding selective and nonselective AA in CKD patients already on RAS.Design, setting, participants, & measurements: MEDLINE, EMBASE, and Renal Health Library were searched for relevant randomized clinical trials in adult CKD patients. Results were summarized using the random-effects model.Results: Eleven trials (991 patients) were included. In comparison to angiotensin-converting enzyme inhibitors (ACEi) and/or angiotensin receptor blockers (ARB) plus placebo, nonselective AA along with ACEi and/or ARB significantly reduced 24 h proteinuria (seven trials, 372 patients, weighted mean difference [WMD] ؊0.80 g, 95% CI ؊1.27, ؊0.33) and BP. This did not translate into an improvement in GFR (WMD ؊0.70 ml/min/1.73m 2 , 95% CI ؊4.73, 3.34). There was a significant increase in the risk of hyperkalemia with the addition of nonselective AA to ACEi and/or ARB (relative risk 3.06, 95% CI 1.26, 7.41). In two trials, addition of selective AA to ACEi resulted in an additional reduction in 24 h proteinuria, without any impact on BP and renal function. Data on cardiovascular outcomes, long-term renal outcomes and mortality were not available in any of the trials.Conclusions: Aldosterone antagonists reduce proteinuria in CKD patients already on ACEis and ARBs but increase the risk of hyperkalemia. Long-term effects of these agents on renal outcomes, mortality, and safety need to be established. Clin J Am Soc Nephrol 4: 542-551, 2009. doi: 10.2215 C hronic kidney disease (CKD) affects 25 to 30 million Americans and several million people across the globe in both developed and developing nations (1,2). A number of treatment options have been shown to delay the progression of kidney damage (3,4). To date, the major impact on delaying the progression of CKD and the risk of end-stage kidney disease (ESKD) has been provided by the use of renin-angiotensin system (RAS) blockers such as angiotensin-converting enzyme inhibitors (ACEi) and angiotensin receptor-blocking agents (ARB). These agents have become standard of care in proteinuric CKD patients (5-8). Both ACEi and ARB significantly reduce proteinuria and the risk of ESKD by about 20 to 30% (9). But this is suboptimal given the higher costs and burden of ESKD (10). Thus, studies exploring interventions for traditional and nontraditional risk factors for CKD are advocated (11).Animal studies have shown that aldosterone has an independent role in the development of hypertensive nephropathy and vascular injury resulting in myocardial and renal fibrosis, and its blockade reduces proteinuria (12-16). In humans, RAS blockade with ACEi or ARB results in an incomplete suppression of serum aldosterone levels, a phenomenon known as "aldosterone escape" (17). When patients are treated with ACEi or ARB, aldosterone levels decrease during...