A novel carrier system that originates from membrane shuttling proteins such as the Drosophila homeobox protein Antennapedia, the HIV-1 transcriptional factor TAT and VP22 from HSV-1 has advantages for targeted delivery compared with standard translocation techniques. This transport system is mediated by so-called cell-penetrating peptides, which consist of short peptide sequences that rapidly translocate large molecules into the cell interior in a seemingly energy- and receptor-independent manner. Cell-penetrating peptides have low toxicity and a high yield of delivery and in the future might become a widely used tool in the field of gene regulation.