Novel targeted compositions which may be used for diagnostic and therapeutic use. The compositions may comprise lipid, protein or polymer gas-filled vesicles which further comprise novel compounds of the general formula L-P-T, wherein L comprises a hydrophobic compound, P comprises a hydrophilic polymer, and T comprises a targeting ligand which targets tissues, cells or receptors, including myocardial cells, endothelial cells, epithelial cells, tumor cells and the glycoprotein GPIIbIIIa receptor. The compositions can be used in conjunction with diagnostic imaging, such as ultrasound, as well as therapeutic applications, such as therapeutic ultrasound.