Purpose: 18F-Fluorodeoxyglucose-positron emission tomography (FDG-PET) is the superior imaging modality for detection of primary and recurrent colorectal cancer compared to magnetic resonance imaging (MRI) or computerized tomography (CT). We investigated the feasibility of developing intraoperative procedures for detection of FDG in tumor deposits in order to assist the surgeon in achieving an optimal reduction of tumor burden.Procedures: Fourteen patients (45-83 years of age) were scanned using FDG-PET followed by Gamma Detection Probe evaluation at laparotomy. One patient did not have a pre-operative FDG-PET scan. The collimated detector probe contained a CdZnTe crystal (7mm diameter x 2mm thick). We used a lower window setting of 200 KeV and an open upper window setting. Fasted patients were given an IV bolus of FDG (4.0-5.7 mCi) 15-20 minutes prior to preparation for surgery. Catheterization and the diuretic Lasix were used to remove FDG activity from the bladder. The time from FDG injection to intraoperative GDP data acquisition varied from 58-110 minutes.Results: In all patients, the GDP detected background activity in normal tissues (aorta, colon, liver, kidney, abdominal wall, mesentery, and urinary bladder). The GDP correctly identified single or multiple tumor foci in 13/14 patients as noted by an audible signal from the control unit (3 S.D. above counts obtained from normal tissues). These tumor foci corresponded to regions of high FDG uptake as seen on FDG-PET scans. The one case that the GDP did not localize was a recurrent mucin pseudomyxoma-producing tumor (acellular, mucinous deposits). Ex vivo GDP evaluations demonstrated significant tumor:normal adjacent tissue activity (audible signals in 6/6 tumor samples tested).Conclusions: These data demonstrate that tumors identified from pre-operative whole-body PET scans can be localized during surgery utilizing a gamma probe detector and FDG.