In one aspect the invention includes an "antibody cocktail" approach to multi-step targeting of an active agent to a target site. This comprises administering multiple targeting moiety conjugates, wherein the targeting moieties are antibodies with nonoverlapping patterns of cross-reactivity for epitopes at the target site and wherein each targeting conjugate has a ligand or anti-ligand that is complementary to a corresponding anti-ligand or ligand on the active agent conjugate. In a further aspect the invention includes a multi-step method for targeting specifically a thrombolytic agent to the site of a thrombus, wherein the targeting moiety may be an annexin. In another aspect annexin may be the targeting moiety in a multi-step method for delivery of an active agent to a site having exposed anionic membrane lipids. In a final aspect, the invention includes specifically the compound biotinamido-N-methylglycyl-seryl-O-succinamido-benzyl DOTA, a chelating structure which may be used to deliver radiometals to a target site.