Patients with diabetic nephropathy (with proteinuria exceeding 100 mg per day while on ace inhibitor ) who are already being treated with ACE-Inhibitor at maximum tolerated dose. For lisinopril this dose usually will be 20-40 mg per day. Patients who are on angiotensin receptor blocker ( ARB ) due to inability to tolerate ace inhibitor ( e.g. due to cough ) will be also considered for the study provided they stay on the same ARB at same dose throughout the study period.