To define the mucin secretion of Barrett's esophagus, 132 biopsy specimens from 37 patients were studied with histochemical stains for mucins. Columnar mucous cells contained largely neutral mucins, but scattered cells in over 70% of the biopsies also produced sialomucins and sulfomucins. Goblet cells contained sialomucins, sulfomucins, or both. The distribution and relative proportions of mucins varied considerably among biopsies and among patients. Barrett's esophagus histochemically represents a heterogeneous, partially differentiated epithelium analogous to incomplete intestinal metaplasia of gastric mucosa.