Abstract: The invention concerns a method for administering bioactive substances to patients at selected sites in the body and remotely promoting delivery of said media to selected organs or tissues in the body. The method comprises providing an administrable formulation comprising, dispersed in an aqueous carrier liquid, liposomes filled with bioactive substances and gas-filled microspheres, injecting said formulation into the circulation of a patient so that it is directed to a site of interest, and applying ultrasound pulses to said site so as to make the gas-filled microbodies explode and the gas confined therein to expand in the carrier liquid, the energy of expansion of said confined gas causing the liposome vesicles to open and release the trapped substances at said site.