Solid lipid nanoparticles (SLNs) offer several technological advantages over standard DNA carriers such as cationic lipids or cationic polymers. However, in the absence of endosomolytic agents such as chloroquine, gene-transfer efficiency mediated by SLN-derived gene vectors consisting of optimized lipid composition remains lower compared to those achieved with standard transfection agents. This protocol describes the incorporation of a dimeric human immunodeficiency virus type-1 (HIV-1) TAT peptide into SLN gene vectors to increase gene-transfer efficiency. This results in higher transfection rates than for standard transfection agents in vitro; the ternary SLN-gene vector complexes usually result in transfection levels equal to or higher than those observed with gene vector complexes formulated with branched polyethylenimine (PEI) 25 kDa. One significant advantage of using this method is the low cytotoxicity of the SLN gene vectors. The application of the gene-transfer technique is limited to relatively low plasmid DNA (pDNA) concentrations of the resulting complexes (10 µg/mL). At higher concentrations, the particles tend to aggregate and precipitate. Therefore, their use for in vivo application, which generally requires high pDNA concentrations, is limited.