Retrograde intrabiliary infusion (RII) has recently been characterized as a safe and effective administration route for liver-Targeted gene delivery. Ef fi cient transgene expression in the liver has been achieved by infusing a variety of gene vectors including adenovirus, retrovirus, lipoplexes, polyplexes, and naked DNA through the common bile duct. Here, we describe the RII technique and key infusion parameters for delivering plasmid DNA and DNA nanoparticles to the rat liver. After RII of plasmid DNA, the level of transgene expression in rat liver is comparable to that achieved by hydrodynamic injection of plasmid DNA, which is considered to be "gold standard" for liver-Targeted gene delivery. RII has also been shown to signi fi cantly enhance the gene delivery ef fi ciency by polymer/DNA nanoparticles in comparison with intravenous and intraportal infusions. This method induces minimal level of cytotoxicity and damage to the liver and bile duct. Due to these advantages, RII has the potential to be used for delivering various gene vectors in clinical setting through the endoscopic retrograde cholangiopancreatography procedure.