Abstract: DIRECT LABELING OF ANTIHEPATOMA MONOCLONAL ANTIBODY FRAGMENT WITH 99Tcm BY AN IMPROVED PRETINNING METHOD Bian Huijie\ Chen Zhinan\ Deng Jinglan①\ Duan Xudong\ Mi li\ Yu Xiaoling\ Xu Liqing(Hepatoma Targeting Research Center, Department of Pathology, Fourth Military Medical University, Xi'an 710032)(① Department of Nuclear Medicine, Xi Jing Hospital, Fourth Military Medical University, Xi'an 710032)Abstract An improved pretinning method of direct labeling of antihuman hepatoma monoclonal antibody fragment with 99Tcm by using stannousglucoheptonate as reducing agent is investigated. The labeling p rocedure is finished within 1.5 h. The number of thiols in the reduced F(ab′) 2 is determined by Ellman,s reagent, and labeling efficiency of 84.2% is obta in ed. Challenge studies indicated that 99mTclabeled HAb18 F(ab′) 2 in EDTA is more stable than in Lcysteine. The imaging result showes a s ignificant tumo r uptake at 24 h postinjection of 99TcmHAb18F(ab′)2. It s uggests that99Tc mHAb18 F(ab′)2 conjugate prepared by this direct method appear an effect ive ability to detect hepatoma in nude mice model.