A multicentric study of Barrett's esophagus (BE) was started in November 1987 to evaluate (1) the prevalence of BE among subjects undergoing upper gastrointestinal endoscopic examination; (2) the pathologic features of BE; and (3) the correlation between BE and early malignant changes. In 157 of 330 patients who underwent multiple standardized biopsies, BE was confirmed with histologic evaluation. Specialized intestinal-type BE was observed in 84 patients. By applying Alcian blue (pH 2.5)-periodate oxidation-Schiff, high-iron diamine-Alcian blue (pH 2.5), and periodate borohydride-saponification-periodate oxidation-Schiff techniques, the intestinal type of BE was subclassified into colonic and ileal types, both complete and incomplete. Fifty cases had incomplete colonic metaplasia with sulphomucins in the columnar cells and 64 had complete colonic intestinal metaplasia, 49 of them containing O-acetylated sialomucins in the goblet cells. These patients are being included in a short-term follow-up. Dysplasia (six low grade, two high grade) was observed in eight patients in areas of intestinal colonic-type epithelium; in these patients, a complete loss of O-acetylated sialomucins in the dysplastic areas and a remarkable reduction of these mucins in the surrounding tissue were observed. The reduction of O-acetylated sialomucins might indicate relative tissue immaturity, which could represent an early sign of neoplastic dedifferentiation. Therefore, the relevance of O-acetylated sialomucin content in BE, first demonstrated in intestinal type, is now evident, although its biologic importance is being studied.