The synthesis of new bifunctional chelating agents (BFCAs) based on the phosphorus hydrazide ligand family for potential Pd-109 labeling of tumor-localizing biomolecules such as proteins/peptides is described. The new BFCAs were achieved in good yields (75-90%) by the reaction of the phosphorus hydrazide PhP(S)(NMeNH2)2 (1) with functionalized aldehydes to yield the Schiff-base products with the following chemical compositions as air-stable crystalline solids : PhP(S)(NMeNH2)(NMeNCHC6H4COOH), 2; PhP(S)(NMeNCHC6H4COOH)2,3; PhP(S)(NMeNH2)(NMeNCHC6H4CH=CHCOOH), 4; PhP(S)(NMeNCHC6H4CH=CHCOOH)2,5. The reactions of three of the new phosphorus hydrazides (2-4) with PdCl2(PhCN)2 resulted in the new Pd(II) metallacycles PhP(S)(NMeNH2)(NMeNCHC6H4COOH).PdCl2, 6; PhP(S)(NMeNCHC6H4COOH)2.PdCl2, 7; and PhP(S)(NMeNH2)(NMeNCHC6H4CH=CHCOOH)-PdCl2, 8. The reactivity of 6 toward n-butylamine has been evaluated as a model for the preparation of new bioconjugates. The structural elucidation of all the new compounds has been carried out by analytical and complete NMR (H-1, P-31) and IR spectroscopic data. As a representative example, the X-ray structure of one of the Pd(II) complexes, 8, has been determined. Crystal data for 8 : monoclinic, space group P2(1)/c, a = 7.981(3) angstrom, b = 21.566(4) angstrom, c = 13.647(5) angstrom, beta = 104.4(2)degrees, Z = 4. The structure was solved by direct methods and was refined to R = 0.055.