Abstract: A chemically defined polymeric carrier comprising a series of .alpha.-amino acids in any combination containing side chains to which diagnostic/therapeutic and chelating agents can be covalently joined through cleavable linkers either directly or covalently joined through cleavable linkers after chemical modification of the side chains. Hydrazone, disulfide, and ester linkages in any combination can be present in the polymeric carrier between the side chains of the .alpha.-amino acids and the agents. The presence of a particular covalent linkage between the side chain and the agent in the carrier is determined by the functional group present in the side chain of the .alpha.-amino acid and the functional group present in the agent. The .alpha.-amino acids with side chains to which agents do not covalently join can function as spacers to minimize interaction between bulky molecules attached to the polymeric carrier. In addition, those .alpha.

Abstract: The specificity of a pharmaceutical agent for a given site of action is increased by covalently bonding the agent via a diphosphate or amidated diphosphate bond to a targeting moiety, preferably a polypeptide specific for the site.

Abstract: Targeting substance-diagnostic/therapeutic agent conjugates joined by stabilized Schiff base or hydrazone linkages are disclosed. In addition, slow release carrier-drug pharmaceuticals are described. The diagnostic and therapeutic conjugates and pharmaceuticals of the present invention provide certain advantages relating to in vivo administration, including controlled release of the active agent at a target site.