Using gastrin-like AOC-tetrapeptide the secretory function of the stomach of Japanese with endoscopically normal gastric mucosa was examined in a multicenter clinical study. Mean one hour secretion volume, mean maximal acidity, and mean maximal acid output were found to be 129.3 +/- 60.0 ml/hr, 103.7 +/- 32.4 mEq/l, and 9.2 +/- 6.9 mEq/hr respectively. Results were analysed according to sex or age by analysis of variance and compared further with the corresponding data reported in the literature.