Gastric epithelial cells, identified in biopsy specimens from individuals with varying degrees of gastritis and cellular atypia, were classified according to morphology and reactivity with an adult tissue-absorbed rabbit antibody to 2nd trimester human fetal tissue. Sections of stomach from normal individuals and patients with superficial gastritis were generally unreactive with this antibody as determined by immuno-peroxidase microscopy. However, a progressive increase in the frequency of antigen-positive gastric epithelial cells was observed during the transition from superficial gastritis to mature metaplasia to dysplasia. Adjunct immunohistologic subclassification of gastric lesions, thus, appears to be possible using a suitably prepared antibody probe. This approach may provide additional parameters necessary for assessment of preneoplastic syndromes and contribute to clinical staging of gastric disease.