Acid secretion in both basal and stimulated states (using augmented histalog test) was studied in 31 normal control patients, 64 duodenal ulcer patients and 101 gastric ulcer patients. Having had the result of acid output study, the 64 DU patients could be classified according to their acid secretion results as 35 DU type I or Normosecretor (54.7%) and 29 DU type II or Hypersecretor (45.3%). For the GU patients which were classified according to the sites of lesions as GU type I (GU above angulus), GU type II (GU associated with DU) and GU type III (GU below the angulus). Their acid output study showed that the GU type I had a rather low BAO and a high MAO close to that of the Normosecretor, but the GU type II and III had their BAO and MAO significantly higher than that of the normal control and close to that of the Hypersecretor. Comparison of acid secretion in this study group to other racial groups showed that the Thai population had acid secretion patterns close to other Asian populations, except that the Chinese in Singapore had a higher proportion of Normosecretor (69.0%) than Hypersecretor (31%). The MAO of the Asian population was found to be lower than that of Europeans.