1. Concentrations of ascorbic acid (ascorbic and dehydro-ascorbic; A + D; measured by the 2,4-dinitrophenylhydrazine method) of nearly three times those of plasma are present in gastric juice samples from patients with normal gastric histology. 2. A significant reduction in gastric juice ascorbic acid (A + D) was observed in patients with chronic gastritis. This reduction in concentration was independent of the grade of gastritis. 3. Concentrations of ascorbic acid (A + D) in gastric biopsy specimens were consistently higher in the antrum than in the body of the stomach. 4. These data demonstrate that considerable quantities of ascorbic acid (A + D) are normally 'secreted' into the stomach. 5. Ascorbic acid (ascorbic only; A; measured by h.p.l.c.) was present predominantly in its biologically active form in the patients with normal gastric histology. However, in patients with gastritis, independent of grade, ascorbic acid was present predominantly in its oxidized, biologically inactive form.