 Interruption of the renin-angiotensin systerm RAS with an angiotensin-converting enzyme ACE inhibitor or an angiotensin II receptor blocker ARB slows the progression of chronic renal insufficiency in the presence or absence of diabetes. Even for advanced chronic renal insufficiency stage 4 CKD, ACE inhibitors and ARBs can still provide renoprotection. Some clinical studies showed that dual RAS blockage seemed to enhance the antiproteinuric effect compared with single-agent ACE inhibitor or ARB and then improve renal survival. However, in the only one randomized controlled trial investigating the renoprotection of combined ACE inhibitor and ARB for mild or moderate chronic renal insufficiency the mean creatinine value is 2.9mgdl, the incidence of hyperkalemia was increased in combination therapy compared with monotherapy. Although increase of hyperkalemia was not statistical significant, it suggested that combination treatment of ACEI and ARB might increase the incidence of hyperkalemia in patients with advanced renal insufficiency. However, it is still undetermined whether combination treatment of ACE inhibitor and ARB is safe as an ACE inhibitor or ARB monotherapy in advanced non-diabetic chronic renal insufficiency stage 4 CKD. The primary aim of the present study is to assess the safety of combined treatment of benazepril an ACE inhibitor or losartan an ARB in non-diabetic patients with advanced renal insufficiency. 