The purpose of this study was to establish a method for imaging the process of gastrointestinal (GI) absorption and subsequent biodistribution in the human body after oral drug administration, using positron emission tomography (PET) with 2-[(18)F]fluoro-2-deoxy-D-glucose ([(18)F]FDG). First, we developed a method to deliver the radiotracer safely into the stomach using soft gelatin capsules to avoid any significant exposure to the pharyngoesophageal region. Second, we performed pharmacokinetic (PK) analyses on time-radioactivity profiles in GI tissues and blood to calculate the gastric emptying and intestinal elimination rate constants and to estimate the fluid volume in the lumen of the small intestine from PET image analysis. This is the first study involving oral administration of a PET probe in humans, and the results demonstrate the high potential of PET technology to investigate the GI absorption and PK profiles of drugs in humans.