Glucagon is used as an anti-motility agent during gastrointestinal tract examinations. We experienced subjects with enhanced 18F-fluorodeoxyglucose (FDG) uptake in whole-body skeletal muscle when conducting positron emission tomography (PET). The subjects had been administered glucagon during gastroscopy just prior to PET. This observation prompted us to perform the present retrospective study to determine whether or not glucagon enhances FDG uptake in skeletal muscle. We randomly selected 30 cases, including subjects who had undergone PET and gastroscopy on the same day as cancer screening procedures, and classified them into three groups. In the NO group (n = 10), no medications were used prior to PET. In the SC group (n = 10), scopolamine butylbromide (10 mg) was intravenously administered during endoscopy. In the GL group (n = 10), glucagon (0.5 mg) was intravenously administered during endoscopy. Both drugs were administered 45-60 min prior to FDG administration. The mean standardized uptake value (SUV) for gluteal muscle was 0.7 ± 0.14, 0.69 ± 0.15, and 0.99 ± 0.7 in the NO, SC, and GL groups, respectively. The SUV in the GL group was highest, but the difference was not statistically significant. In the subject with the highest SUV (3.04; GL group), the quality of the oncologic PET image was impaired, perhaps because of a relative decrease of FDG distribution in the chest and abdomen. Because previous literature showed that via hyperglycemia and hyperinsulinemia glucagon has the effect of increasing FDG uptake in skeletal muscle, the use of glucagon should be avoided just prior to FDG PET, although in our subjects, no statistical proof that glucagon enhances FDG uptake in skeletal muscle was obtained.