The production of HLA antibodies (Abs) has been reported to have predictive value for graft failure. We examined whether the presence of HLA Abs reflects the patient's clinical status after renal transplantation. Among sera from 243 living donor renal transplant recipients with a functioning graft (6 months to 21 years after transplantation), 27 sera were positive for HLA Abs (27/243: 11.2%). Incidence of acute rejection (59.3 vs 35.6%), serum creatinine (1.70 +/- 0.67 vs 1.48 +/- 0.78 mg/dL) and positive rate of urine protein (29.6 vs 25.0%) were not significantly different between 27 positive HLA Abs and 216 Negative. However, considering the status of HLA Abs before and after transplantation, serum creatinine and positive urine protein in negative to positive (Neg to Pos: n = 12) and positive to positive patients (Pos to Pos: n = 15) were 1.98 +/- 0.70 vs 1.48 +/- 0.58 mg/dL (p = 0.05) and 58.3% vs 6.7% (p = 0.004), respectively, indicating that de novo production of HLA Abs was related to higher serum creatinine and urine protein levels, which appeared to progress to renal failure sooner. Among 38 sera with positive HLAAbs, donor specific HLA Abs could be detected in 6/12 (50%) after graft failure, while they were detected only in 2/26 (7.7%) of recipients with functioning graft. The measurement of HLA Abs after transplantation is thought to provide valuable information on prognosis and treatment of the graft. However, simple and economical monitoring methods should be explored in cases of positive HLA Abs before transplantation, because de novo production of HLA Abs would be difficult to detect after transplantation.