OBJECTIVE: To investigate the effects of hypochlorhydria and acidic drink ingestion on protein-bound vitamin B12 absorption in elderly subjects. METHODS: Absorption of protein-bound vitamin B12 was examined in elderly normal subjects (n = 8), and in hypochlorhydric subjects due to omeprazole treatment (n = 8) or with atrophic gastritis (n = 3). Subjects underwent absorption tests of protein-bound vitamin B12 ingested with water, cranberry juice and 0.1 N hydrochloric acid. RESULTS: Protein-bound vitamin B12 absorption was lower in the omeprazole-treated group (0.50%) compared to the normal group (1.21%; p < 0.001). With cranberry juice ingestion, the omeprazole-treated group showed an increase in absorbed protein-bound vitamin B12 (p = 0.025). With dilute hydrochloric acid ingestion, there was a further increase in vitamin B12 absorption (p < 0.001). CONCLUSION: Omeprazole causes protein-bound vitamin B12 malabsorption, and ingestion of an acidic drink improves protein-bound vitamin B12 absorption.