This prospective study was designed to investigate the clinically significant level of parvovirus B19 viral load using quantitative real-time (RT) polymerase-chain reaction (PCR) in kidney transplantation (KT) recipients. One hundred forty-three adult recipients who underwent their first KT between November 2003 and October 2005 were enrolled. Six blood samples (the first taken preoperatively, subsequent samples taken every 4 weeks for 20 weeks) were taken from each patient for parvovirus B19 DNA RT-PCR analysis. All recipients were diligently followed for 1 year post-transplant. One hundred sixty-eight of the 715 (23.5%) postoperative samples were positive for parvovirus B19 PCR. Eighty-four of the 143 KT recipients (58.7%) showed at least one positive PCR. Sixteen of the 143 (11.1%) KT recipients had sustained severe anemia (SSA) with hemoglobin lower than 7.0 g/dl, after 4 weeks post-transplant. The incidence of SSA in recipients with a titer higher than 1 x 10(6) copies/5 microl whole blood was significantly higher than those with a negative or low titer (P < 0.001, positive predictive value 84.6%, negative predictive value 96.2%). In conclusion, a high titer of parvovirus B19 DNA higher than 1 x 10(6) copies/5 microl whole blood in KT recipients was related with SSA after 4 weeks post-transplant.