Endoscopic and biopsy findings of the esophagus, stomach, duodenum, and colorectum were studied in 37 patients with amyloidosis involving the gastrointestinal tract. Endoscopic examinations revealed fine granular appearance, polypoid protrusions, erosions, ulcerations, and mucosal friability in many cases. These findings were most marked and noticed most often in the second portion of the duodenum. The frequency of amyloid deposition in the biopsy specimens was as follows; 100% in the duodenum, 95% in the stomach, 91% in the colorectum, and 72% in the esophagus. The degree of amyloid deposition in the duodenum, which was the highest of the entire gastrointestinal tract, significantly correlated with the frequency of endoscopic findings such as fine granular appearance and polypoid protrusions. Therefore, the two endoscopic findings described above are characteristic of this disease and may reflect amyloid deposition in the mucosa or submucosa of the alimentary tract. Our results indicate that for a diagnosis of amyloidosis, it is important to examine the upper gastrointestinal tract, especially the duodenum, using endoscopy and biopsy techniques.