A barium swallow is a diagnostic test that involves a series of X-rays of the esophagus, stomach, and duodenum during and after drinking a barium solution. The duodenum is the first part of the small intestine; and the esophagus, stomach, and duodenum are collectively called the upper gastrointestinal (GI) tract or upper digestive system. You may also hear doctors refer to a barium swallow as an upper GI series or a barium meal.