The present invention provides methods for retaining and expressing physiologically active substances in a target tissue-specific-manner, by administering the physiologically active substances to target submucous tissue. Specifically, the present inventors demonstrated that, when physiologically active substances were directly administered into submucous tissues without using a carrier, the physiologically active substances were effectively and safely retained at the administration sites over long periods without loss and diffusion, and produced the effect acting in a reservoir-like fashion. The physiologically active substances administered as described above were demonstrated to produce the therapeutic effect without having an influence on organs other than the administered organ.