RNA interference, the sequence-specific silencing of gene expression by introduction of short interfering RNA (siRNA) is a powerful tool that that the potential to act as a therapeutic agent and the advantage of decreasing toxic effects on normal tissue sometimes seen with conventional treatments i.e. small molecule inhibitors. Naked, unmodified siRNA is poorly taken up by cells and is subject to degradation when exposed to blood proteins during systemic administration. It has also been shown to produce non-specific immune response as well as having the potential to generate 'off-target' effects. Therefore there is a requirement for a delivery system to not only protect the siRNA and facilitate its uptake, but additionally to offer the potential for targeted delivery with an aim of exploiting the high specificity afforded by RNA interference. Cationic liposomes are the most studied, non-viral delivery system used for nucleic acid delivery. As such, the use of cationic liposomes is promising for siRNA for delivery. Furthermore, polyethylene glycol (PEG) can be incorporated into the liposome formulation to create sterically stabilized or 'stealth' liposomes. Addition of PEG can reduce recognition by the reticuloendothelial system (RES) thereby prolonging circulation time. Here we describe a methodology for the complexation of siRNA with cationic liposomes and PEGylated liposomes using two protocols: mixing and encapsulation. Moreover, the different formulations are compared head to head to demonstrate their efficacy for gene silencing. © 2009 Elsevier Inc. All rights reserved.