The location of a small lesion must be precisely identified during laparoscopic surgery. A gamma probe that is usually used for navigating sentinel lymph nodes was evaluated for its usefulness in locating small gastrointestinal lesions (14 gastric and 10 colonic). A total of 2 mCi of a Tc(99m)-labeled rhenium colloid was injected endoscopically around a tumor 16 h prior to surgery. During operation, the abdominal cavity was scanned using a handheld gamma probe (Navigator GPS, Tyco HealthCare, Norwalk, CT, USA). In all cases, the injection site was identified as the highest spot in the abdominal cavity, with 2585 counts per second on average (range, 910-8800 counts per second). The highest count in a lymph node was 637 per second on average. The gamma probe is a useful tool for identifying small gastrointestinal lesions during open and laparoscopic operations.