Using a new synthetic gastrin-like AOC-tetrapeptide (t-amyloxy•carbonyl•Try•Met•Asp •Phe•NH2), a multicenter pilot study was carried out to assess its clinical utility for the analysis of gastric conditions. Computer analysis revealed that 4μg of the drug per kg body weight yielded the maximal acid secretory response, which was characterized by an earlier appearance of a higher maximal response value than with betazole hydrochloride of 1mg per kg body weight. Maximal AOC-tetrapeptide test enabled discrimination between cases of endoscopically normal gastric mucosa and those of duodenal ulcer relatively well, but the differential diagnosis was unsatisfactory in cases of some endoscopically distinguishable conditions of the stomach such as normal stomach, atrophic gastritis, gastric ulcer and duodenal ulcer. It is particularly noteworthy that no side effect was observed during the entire experiment.