Serial morphological, secretory, and serological observations of a patient with Ménétrier's disease disclosed hypergastrinemia, antibodies to parietal cells and dietary substances, and an acute reduction of gastrointestinal protein loss after atropine administration. Transformation of the gastric mucosa from hypertrophy to atrophic gastritis was associated with disappearance of the protein-losing gastroenteropathy and serum antibodies and reduction of the serum gastrin concentration.