The invention relates to an RNA comprising at least one open reading frame (ORF) and comprising at least one modification, which increases the expression of the encoded peptide or protein. Furthermore, the invention relates to the medical use of such a modified RNA administered to a subject by jet injection. The invention relates further to a pharmaceutical composition and to a kit of parts comprising said modified RNA for administration by jet injection, preferably for use in the field of gene therapy and/or genetic vaccination. Additionally, the invention relates to a method for enhancing the (localized) expression of RNA-encoded peptides or proteins in the dermis or muscle (of a mammal) comprising administering the modified RNA by jet injection. And finally, the invention relates to a method of treatment comprising administering the modified RNA by jet injection to a subject in need thereof.