If a colonoscopy does not reveal a source for your diarrhea, the most likely next step in the evaluation would be to look at the small intestine, with either a small bowel x-ray or a capsule endoscopy (where a small pill camera is ingested).
As you can see from the above, the investigation of diarrhea can be a long, complicated process. After a thorough history, depending on your age, family history and associated symptoms, your doctor will decide the approach that is most appropriate for you.
What is a colonoscopy, you ask. Find out here.
Read what a gastroenterologist has to say.

