[en] Addition of sulfhydryl groups with 2-iminothiolane (2-IT) is an important new method for labelling monoclonal antibodies (mAb) and fragments with ^99mTc. F(ab')₂ fragments were prepared by digestion of 1B7.11 and BCD-F9 with pepsin. Optimal conditions for labelling 20-100 μg mAb or F(ab')₂ involved a 2000:1 molar ratio of 2-IT: protein in phosphate buffer pH 7.4 for 30 min followed by addition of^99m Tc-pertechnetate and stannous glucoheptonate. Recovered yields were >70% and radiochemical purities were >90% with a total preparation time of <90 min