Summary The gastric acid response and the buffer capacity of the stomach were measured in 30 control subjects and 22 duodenal ulcer patients in response to a masticatory (solid) and a non-masticatory (homogenized) meal having the same chemical composition. The peak acid output values were equal after a masticatory and after a non-masticatory diet in control subjects (masticatory 18.1 ± 1.2, non-masticatory 15.7 ± 1.3 mmol/hr) as well as in duodenal ulcer patients (masticatory 35.7 ± 1.5, non-masticatory 33.7 ± 1.1 mmol/hr). The buffer capacity of the stomach contents 1 hr after the meal was significantly greater after a masticatory diet than a non-masticatory diet in both controls (14.6 ± 1.4 and 9.0 ± 1.9 mmol) and in duodenal ulcer patients (9.5 ± 1.5 and 7.5 ± 1.2 mmol). Duodenal ulcer patients had a significantly lower buffer capacity compared with controls. Masticatory diets may play a part in protecting individuals from developing duodenal ulcer.