Melanosis of the esophagus. An endoscopic, histochemical, and ultrastructural study. Endoscopic, histological, and ultrastructural features of 21 cases of esophageal melanosis are described. These cases were detected during 1000 consecutive routine upper gastrointestinal endoscopies. Staining characteristics and ultrastructure of the pigment contained in the endoscopically visible lesions were found to be similar to those of true melanin. 