This invention relates to new peptide-based compounds and their use in therapeutically effective treatments as well as for diagnostic imaging techniques. More specifically the invention relates to the use of such peptide-based compounds used as targeting vectors that bind to receptors associated with angiogenesis, in particular the .alpha.v.beta.3 integrin receptor. Such contrast agents may thus be used for diagnosis of for example malignant diseases, heart diseases, inflammation-related diseases, rheumatoid arthritis and Kaposi's sarcoma. Moreover such compounds may also be used in therapeutic treatment of these diseases.