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 immunoperoxidase microscopy. 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 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.