This study consists of 959 consecutive patients in whom endoscopic biopsies were taken according to a protocol that permitted mapping and measurement of epithelial types in the gastroesophageal region. The epithelial types were classified as normal (oxyntic and squamous) and questionably abnormal (oxyntocardiac, cardiac, intestinal) by strict histologic criteria. Patients were classified into four groups based on the length of histologically defined abnormal glandular epithelium in the measured biopsies. A total of 811 (84.6%) patients had 0 to 0.9 cm of questionably abnormal columnar epithelium between normal oxyntic mucosa and squamous epithelium. Of these, 161 (19.9%) patients had no abnormal epithelium, 158 (19.4%) patients had oxyntocardiac mucosa, 372 (45.9%) patients had cardiac mucosa, and 120 (14.8%) patients had intestinal metaplasia. A total of 148 (15.4%) patients had >or=1 cm of abnormal columnar epithelium. All but one patient in this group had cardiac or intestinal epithelia. The prevalence of intestinal epithelium increased progressively with increasing length of abnormal columnar epithelium, being present in 70.4% in the 1- to 2-cm group, 89.5% in the 3- to 4-cm group, and 100% with in the >or=5 cm group. We propose a histologic grading system of biopsies based on these findings.