A radiohalogen-labeled protein having the structure: wherein Hal is a radiohalide isotope selected from 123 I, 124 I, 125 I, 131 I, and 211 At; L is a linker selected from -(C 1 -C 12 alkylene)-C NR-(C 1 -C 12 alkylene)-, - (C 1 -C 12 alkylene)-C NR-(C 1 -C 12 alkylene)O-, -(C 1 -C 12 alkylene)-C NR-(C 1 -C 12 alkylene)-C CH 2 -, -(C 1 -C 12 alkylene)-C N -, -(C 1 -C 12 alkylene)-C NR-(C 2 -C 8 alkenylene)-, -(C 1 -C 12 alkylene)-C NR-(C 2 -C 8 alkynylene)-,-(C 1 -C 12 alkylene)-C NR(CH 2 CH 2 O) n -, -(C 1 -C 12 alkylene)-C -, -(C 1 -C 12 alkylene)-C NR(CH 2 CH 2 O) n CH 2 C -, and -(C 1 -C 12 alkylene)-C NR(CH 2 CH 2 O) n CH 2 -, where n is 1 to 6, R is H, C 1 -C 12 alkyl, or C 6 -C 20 aryl, and alkylene, alkenylene, alkynylene, alkyl, and aryl are optionally substituted with one or more groups selected from F, Cl, Br, I, -CH 3, -CH 2 CH 3, -CH(CH 3) 2, - CH 2 CH(CH 3) 2, -CH 2 NH 2, -CH 2 CH 2 NH 2, -CH 2 CHCH 2 NH 2, -CH 2 CH(CH 3)NH 2, - CH 2 OH, -CH 2 OCH 3, -CH 2 CH 2 OH, -CH 2 CH 2 OCH 3, -C(CH 3) 2 OH, -CH CH(CH 3) 2, -C(CH 3) 2 CH 2 OH, -CH 2 CH 2 SO 2 CH 3, -CN, -CF 3, -CO 2 H, -COCH 3, -CO 2 CH 3, - CO 2 C(CH 3) 3, -COCH CH 3, -CONH 2, -CONHCH 3, -CON(CH 3) 2,-C(CH 3) 2 CONH 2, -NO 2, -NH 2, -NHCH 3, -N(CH 3) 2, -NHCOCH 3, -N(CH 3)COCH 3, - NHS 2 CH 3, -N(CH 3)C(CH 3) 2 CONH 2, -N(CH 3)CH 2 CH 2 S 2 CH 3, =O, -OH, -OCH 3, -OP 3, -S 2 N(CH 3) 2, -S 3, -SCH 3, and -S 2 CH 3; Z is selected from X, S, NH, CH 2 C, C, (CH 2 CH 2 O) n CH 2 C, NHC, NHC, OP 2, (CH 2 CH 2 O) n CH 2 X, and (C 1 -C 12 alkylene)X, where X is and PRO is a protein selected from an antibody, an interferon, a lymphokine, a cytokine, a peptide, a hormone, and a growth factor. Hal is a radiohalide isotope selected from 123 I, 124 I, 125 I, 131 I, and 211 At; L is a linker selected from -(C 1 -C 12 alkylene)-C NR-(C 1 -C 12 alkylene)-, - (C 1 -C 12 alkylene)-C NR-(C 1 -C 12 alkylene)O-, -(C 1 -C 12 alkylene)-C NR-(C 1 -C 12 alkylene)-C CH 2 -, -(C 1 -C 12 alkylene)-C N -, -(C 1 -C 12 alkylene)-C NR-(C 2 -C 8 alkenylene)-, -(C 1 -C 12 alkylene)-C NR-(C 2 -C 8 alkynylene)-,-(C 1 -C 12 alkylene)-C NR(CH 2 CH 2 O) n -, -(C 1 -C 12 alkylene)-C -, -(C 1 -C 12 alkylene)-C NR(CH 2 CH 2 O) n CH 2 C -, and -(C 1 -C 12 alkylene)-C NR(CH 2 CH 2 O) n CH 2 -, where n is 1 to 6, R is H, C 1 -C 12 alkyl, or C 6 -C 20 aryl, and alkylene, alkenylene, alkynylene, alkyl, and aryl are optionally substituted with one or more groups selected from F, Cl, Br, I, -CH 3, -CH 2 CH 3, -CH(CH 3) 2, - CH 2 CH(CH 3) 2, -CH 2 NH 2, -CH 2 CH 2 NH 2, -CH 2 CHCH 2 NH 2, -CH 2 CH(CH 3)NH 2, - CH 2 OH, -CH 2 OCH 3, -CH 2 CH 2 OH, -CH 2 CH 2 OCH 3, -C(CH 3) 2 OH, -CH CH(CH 3) 2, -C(CH 3) 2 CH 2 OH, -CH 2 CH 2 SO 2 CH 3, -CN, -CF 3, -CO 2 H, -COCH 3, -CO 2 CH 3, - CO 2 C(CH 3) 3, -COCH CH 3, -CONH 2, -CONHCH 3, -CON(CH 3) 2,-C(CH 3) 2 CONH 2, -NO 2, -NH 2, -NHCH 3, -N(CH 3) 2, -NHCOCH 3, -N(CH 3)COCH 3, - NHS 2 CH 3, -N(CH 3)C(CH 3) 2 CONH 2, -N(CH 3)CH 2 CH 2 S 2 CH 3, =O, -OH, -OCH 3, -OP 3, -S 2 N(CH 3) 2, -S 3, -SCH 3, and -S 2 CH 3; Z is selected from X, S, NH, CH 2 C, C, (CH 2 CH 2 O) n CH 2 C, NHC, NHC, OP 2, (CH 2 CH 2 O) n CH 2 X, and (C 1 -C 12 alkylene)X, where X is and PRO is a protein selected from an antibody, an interferon, a lymphokine, a cytokine, a peptide, a hormone, and a growth factor.