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Purpose: The aim of this study was to compare the performances pretargeted immunoPET 68 Ga-PETimaging ( 68 Ga-pPET) with anti carcino-embryonic antigen (CEA) and anti-histamine-succinyl-glycine (HSG) recombinant humanized bispecific monoclonal antibody (TF2) and 68 Ga-labeled HSG peptide (IMP288) to conventional 18 FDG-PET in an orthotopic murine model of liver metastases of human colonic cancer., Methods: Hepatic tumor burden following intra-portal injection of luciferase-transfected LS174T cells in nude mice was confirmed using bioluminescence. One group of animals was injected intravenously with TF2 and with 68 Ga-IMP288 24 hours later (n=8). Another group received 18 FDG (n=8), and a third had both imaging modalities (n=7). PET acquisitions started 1 hour after injection of the radioconjugate. Biodistributions in tumors and normal tissues were assessed one hour after imaging., Results: Tumor/organ ratios were significantly higher with 68 Ga-pPET compared to 18 FDG-PET ( P <0.05) with both imaging and biodistribution data. 68 Ga-pPET sensitivity for tumor detection was 67% vs. 31% with 18 FDG PET ( P =0.049). For tumors less than 200 mg, the sensitivity was 44% with 68 Ga-pPET vs. 0% for 18 FDG PET ( P =0.031). A strong correlation was demonstrated between tumor uptakes measured on PET images and biodistribution analyses (r 2 =0.85)., Conclusion: 68 Ga-pPET was more sensitive than 18 FDG-PET for the detection of human colonic liver metastases in an orthotopic murine xenograft model. Improved tumor/organ ratios support the use of pretargeting method for imaging and therapy of CEA-expressing tumors., Competing Interests: CONFLICTS OF INTEREST Dr. Goldenberg is an inventor of DNL, and was an officer and employee of Immunomedics, Inc., and of IBC Pharmaceuticals, Inc. He retired from IBC Pharmaceuticals and from Immunomedics after this article was submitted for publications. The other authors have no disclosures to report.