The present invention concerns an in vivo method for introducing an mRNA molecule (which is not associated with a carrier) into the cytosol of a cell(s) in a subject, by the use of photochemical internalization, wherein the photosensitising agent is a sulphonated meso-tetraphenyl chlorin, sulfonated tetraphenylporphine or a di- or tetrasulfonated aluminium phthaiocyanine used in an amount of 0.0001 to 1µg. The method may be used to express a polypeptide in the subject. The invention is also directed to pharmaceutical compositions containing the photosensitising agents and the mRNA and uses of the molecules in therapy, e.g. to treat or prevent cancer or an infection.
