AIM:To directly radiolabel an anti-hepatoma mAb fragment HAb18 F(ab')(2) with (99m)Tc by stannousreduced method, and assess the stability, biodistribution and radioimmun oimaging (R II).METHODS:Immunoreactive fraction was determined according to Lindmo's method. Ellman's reagent was used to determine the number of thiols in the reduced F(ab') (2). Labeling efficiency and homogeneity were measured by paper chromatography, sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography. Challenge assay involved the incubation of aliquots of labeled antibody in ethylenediaminetetraacetate (EDTA) and L-cysteine (L-cys) solutions with different molar ratio at 37° for 1h, respectively. Investigations in vivo utilized nude mice bearing human hepatocellular carcinoma (HHCC) xenografts with gamma camera imaging and tissue biodistribution studies at regular intervals.RESULTS:The labeling procedure was finished within 1.5h compared with the pretinning method which would take at least 21h. In vitro studies demonstrated that the radiolabeled mAb fragment was homogeneous and retained its immunoreactivity. Challenge studies indicated that (99m)Tc-labeled HAb18 F(ab') (2) in EDTA is more stable than in L-cys. Imaging and biodistribution showed a significant tumor uptake at 24h post injection of (99m)Tc-labeled HAb18 F(ab') (2). The blood, kidney, liver and tumor uptakes at 24h were 0.56 ± 0.09, 56.45 ± 11.36,1.43 ± 0.27 and 6.57 ± 3.01 (%ID/g) respectively.CONCLUSION:(99m)Tc-HAb18 F(ab') (2) conjugate prepared by this direct method appears to be an effective way to detect hepatoma in nude mice model.