Upper gastrointestinal series is the X-ray examination of the upper gastrointestinal tract that includes oesophagus stomach and the first part of the small intestine called the duodenum. The gastrointestinal tract is made visible on X-ray film by a liquid suspension which is usually a barium soluble contrast. Barium is a dry white chalky powder and is a good X-ray absorber. Barium appears white on the X-ray film. When you swallow the barium drink it coats the inside walls of the gastrointestinal tract and the doctor can clearly see the function size and shape of the organs on the X-ray film.