We actively performed renal allograft biopsies on 87 living donor renal transplant recipients presenting with stable serum creatinine but showing newly developed recurrent microscopic hematuria with a small amount of proteinuria during the maintenance phase of immunosuppression and found definite pathological lesions in 56 cases (64%). Chronic rejection of a mild grade (n = 27) and various kinds of glomerulonephritis (n = 27) were the major pathological diagnoses, and from 14 cases singular or complicated cyclosporine (CsA) toxicity was found. Twenty-four out of the 27 glomerulonephritis cases were IgA nephropathy, which is the most common glomerulonephritis in Korea. Through this study, the authors found chronic rejection or glomerulonephritis even in grafts which are generally considered to be normal. CsA nephrotoxicity, which was not expected clinically, could be found. In summary, renal allograft biopsy on patients, even with stable graft function when they start to show microscopic hematuria with or without a small amount of proteinuria, should be perfomed to document the early intragraft events if there are no medical contraindications.