We examined 23 patients with columnar-lined esophagus (2 with long segment and 21 with short segment) endoscopically. After staining with Lugol's iodine solution, squamous islands were identified in the columnar mucosa in 18 (78%) of the 23 patients. When biopsy specimens were obtained from these islands, esophageal glands proper or their ducts were seen in 12 (67%) of the 18 cases. Because the identification of esophageal glands proper is a definite indicator that a piece of biopsy tissue is of esophageal origin, a diagnosis of columnar-lined esophagus could be made purely on the basis of the histological findings in these biopsy specimens of squamous islands. This was the case in 12 (52%) of the 23 patients examined in this study. Staining with Lugol's iodine solution, with subsequent biopsy of stained squamous islands, may assist in the diagnosis of short-segment columnar-lined esophagus. We also conclude, on the basis of our study, that columnar metaplasia of the esophagus cannot develop by direct outgrowth of epithelium from the ducts of esophageal glands proper. In addition, intestinal metaplasia was not always observed in the columnar mucosa around the duct orifices. From a practical point of view, biopsy specimens from columnar-lined mucosa of the esophagus do not always show intestinal metaplasia (specialized intestinal metaplasia).