A barium enema is a test used to help diagnose problems with the large intestine (colon). The test is also called a lower gastrointestinal (GI) series. For the test, a health care provider inserts a special tube into your rectum. Then, liquid barium is put into your rectum through the tube. The barium coats the inside of your colon and rectum so that they can be seen more clearly on an x-ray. An x-ray is taken of your lower GI tract. The x-ray pictures are studied to check for any problems, such as an enlarge ment of the intestine, blockage of the intestine, or ulcers.