Unaided cellular uptake of RNA interference agents such as antisense oligonucleotides and siRNA is extremely poor, and in vivo bioavailability is also limited. Thus, effective delivery strategies for such potential drugs are in high demand. Recently, a novel approach using a class of short cationic peptides known as cell-penetrating peptides (CPPs) is attracting wide attention for a variety of biologically active molecules. CPP-mediated delivery is typically based on the covalent conjugation of the (therapeutic) cargo to CPPs, and is particularly relevant for the delivery of noncharged RNA interference agents such as peptide nucleic acids (PNAs) and morpholino oligomers. Although chemical conjugation to a variety of CPPs significantly improves the cellular uptake of PNAs, the bioavailability (and hence antisense activity) of CPP-PNA -conjugates is still highly limited by endocytotic entrapment. We have found, however, that this low -bioavailability can be significantly improved by chemical conjugation to a lipid domain ("Lip," such as a fatty acid), thereby creating "CatLip"-conjugates. The cellular uptake of these conjugates is conveniently evaluated using a sensitive cellular assay system based on a splicing correction of a mutated luciferase gene in HeLa pLuc705 cells by targeting antisense oligonucleotides to a cryptic splice site. Further improvement in the delivery of CatLip-PNA conjugates is achieved by using auxiliary agents/treatments (e.g., chloroquine, calcium ions, or photosensitizers) to induce endosomal disruption.