Antisense oligonucleotides have a large therapeutic potential. However, the low effectiveness with which they cross biological membranes limits their clinical development. Many delivery strategies were proposed to circumvent this problem but the majority remain inadapted to an in vivo use. During this last decade, several peptides able to cross the plasma membrane were characterized. Gathered under the name of Cell Penetrating Peptides, these peptides are polycationic and sometimes amphipatic. Our work, using luciferase splice correction cells model, indicates that these CPPs and their conjugates to PNA or PMO remain blocked in endocytic vesicles. Endosomolytic agents, like chloroquine, promote the endosomal escape and improves the splice correcting efficency. It is now admitted that the development of new peptides vectors with an intrinsic endosomolytic property would constitute a major step in the field of the delivery. Two conjugates (R-Ahx-R)4-PMO and R6Pen-PNA, effectively correct splicing without addition of chloroquine. The mechanistic studies indicate that these conjugates are internalised in the cells by an endocytotic mechanism. The structure-activiy studies indicate a correlation between the affinity of CCP-ON to the heparan sulphate as well as theirs hydrophobicities and the effectiveness of correction. Work on the animals models showed a broad biodisponibility of (R-Ahx-R)4-RMO.