Rapid allograft infection complicates liver transplantation (LT) in patients with hepatitis C virus (HCV). Pegylated interferon-alpha and ribavirin therapy after LT has significant toxicity and limited efficacy. The effect of a human monoclonal antibody targeting the HCV E2 glycoprotein (MBL-HCV1) on viral clearance was examined in a randomized, double-blind, placebo-controlled pilot study in patients infected with HCV genotype 1a undergoing LT. Subjects received 11 infusions of 50 mg/kg MBL-HCV1 (n=6) or placebo (n=5) intravenously with three infusions on day of transplant, a single infusion on days 1 through 7 and one infusion on day 14 after LT. MBL-HCV1 was well-tolerated and reduced viral load for a period ranging from 7 to 28 days. Median change in viral load (log10 IU/mL) from baseline was significantly greater (p=0.02) for the antibody-treated group (range -3.07 to -3.34) compared to placebo group (range -0.331 to -1.01) on days 3 through 6 posttransplant. MBL-HCV1 treatment significantly delayed median time to viral rebound compared to placebo treatment (18.7 days vs. 2.4 days, p