This article suggests that cell lineages of defined phenotype arise within gastrointestinal epithelia exposed to acid hypersecretion-the ulcer-associated cell lineage (UACL), "gastric metaplasia" and that of Barrett's esophagus. Detailed study of both the histogenesis and secretory peptide phenotype of the UACL and gastric metaplasia reveal an origin from newly-formed ducts and Brunner's gland ducts, respectively. It is suggested that Barrett's epithelium arises directly from the epithelium of the cardiac esophageal glands, and that these three ductal epithelia are the origins of these three important adaptive phenomena to gastric hypersecretion.