The invention provides, in a general sense, a new labeling strategy employing .sup.99mTc chelated with ethylenedicysteine (EC). EC is conjugated with a variety of ligands and chelated to .sup.99mTc for use as an imaging agent for tissue-specific diseases. The drug conjugates of the invention may also be used as a prognostic tool or as a tool to deliver therapeutics to specific sites within a mammalian body. Kits for use in tissue-specific disease imaging are also provided.