PromoFectin shows lowest residual toxicity and is therefore ideally suited even for transfection of very sensitive cells yielding optimal transfection efficiencies and gene expression. Transfection with PromoFectin requires no medium change and it can be used for highly effective delivery of plasmid DNA as well as oligonucleotides and siRNA into adherent and non-adherent cells. It compacts and protects the nucleic acid of interest and the endocytosed PromoFectin/Nucleic acid complexes are entering the cell very efficiently - releasing the intact nucleic acids very rapid and almost completely into the cytosol. Moreover, PromoFectin also favors DNA trafficking to the cell nucleus. Other PromoFectin variants for transfection of e.g. neuronal or insect cells and the delivery of siRNA, oligonucleotides and proteins into cells are also available.