Barrett's esophagus is a condition in which the normal squamous epithelium of the esophagus has been replaced by an abnormal red columnar epithelium called specialized intestinal metaplasia. Specialized intestinal metaplasia is red like normal stomach tissue but does not look like stomach tissue under the microscope. Therefore, a biopsy (taking piece of tissue from the esophagus) is needed to diagnose Barrett's esophagus.