The upper gastrointestinal (GI) series examines the upper and middle portions of the GI tract. The person being tested swallows a "shake" of barium and water (barium contrast material) followed by gas-producing crystals. The doctor then tracks the progress of the barium through the esophagus, stomach, and small intestine using fluoroscopy connected to a video monitor. Several X-ray pictures are usually taken at different times and from different directions.