The present invention concerns a method for intracellular delivery of isolated naked nucleic acids into isolated biological tissue or organ, said method comprising at least the steps of: a/ contacting said tissue or organ with an efficient amount of at least one active corticosteroid, and contacting said animal cells treated in step a/ with an efficient amount of isolated naked nucleic acids, said step a/ being carried out for a period of time ranging from at least five minutes to at most two hours and being immediately followed by step b/.
