Amino-dextran-10 (ADX-10) was partially oxidized to polyaldehyde-ADX which was then reacted with deferoxamine (DFO) to form a Schiff's base and converted into a secondary amine, ADX-DFO (I) with ten moles of DFO per mole of ADX. ADX-DFO was chelated with Indium or 111In to yield ten moles of In or 111In per mole of ADX-DFO. A selective maleimide derivatization of (I) with sulfosuccinimidyl-4-(p-maleimidophenyl) butyrate yielded (II), which contained 3 moles of maleimide groups per mole of (II). The sulfhydryl-amidinium derivatization of the monoclonal antibody (MoAb) TP41.2 with 2-IT produced (III). Compounds (II) and (III) were combined to form the thioether space-arm linkage of (IV), which was subsequently radiolabeled with 111In to yield (V). MoAb-DFO-111In, (VI), was also prepared for a control study. Direct cell binding revealed the immunoreactivity of (V) to be 79.7% and that of (VI) to be 60.3%. The in vitro stability of (V) at 4, 24, and 48 hours resulted in 1.7%, 7.0% and 16.0% hydrolysis respectively, as compared with 2.1%, 8.7% and 18.5% hydrolysis of the control (VI), at the same time intervals. In a biodistribution study in non-tumor rats at 4, 24, and 48 hours post-injection, the liver concentration at 48 hours was 2.97% (ID/g) for (V) and 4.84% (ID/g) for (VI). This novel technique for radiolabeling antibodies allows for a high level of radiometallic labeling, preservation of immunoreactivity, and reduction of uptake by the liver.