Magnetic targeted carriers (MTC) are magnetically susceptible microparticles that can be physically targeted to a specific site. MTC were radiolabeled with (111)In using three different methods. Reaction parameters were investigated in order to optimize the final properties of the labeled MTC. The reaction parameters studied were chelation agent, chelation time, temperature, radiolabeling time, solvent, and molar ratios. A 97.7 +/- 0.9% binding efficiency and plasma stability of 92.6 +/- 0.1% over 7 days were achieved when 2-p-aminobenzyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra-acetic acid (ABz-DOTA) was used as the chelating agent. A preliminary animal biodistribution study confirmed the binding stability. The labeling of the MTC with the diagnostic isotope (111)In was undertaken to allow for quantitative imaging and dosimetry prior to therapy with (90)Y radiolabeled MTC.