The amino acids in human gastric juice were measured in the hospital control (n = 9), gastric ulcer (n = 10), duodenal ulcer (n = 12), gastroduodenal ulcer (n = 9), and gastric cancer patients (n = 16) by high performance liquid chromatography, and the total of 15 kinds of amino acids was correlated with value determined by Ninhydrin method. The patients with gastric cancer had elevated levels of all amino acids, especially alanine, leucine, valine and threonine. In all but the gastric cancer disease groups, the aromatic amino acids, phenylalanine and tyrosine as well as leucine were at high levels in 1 5 amino acids. The different patterns of amino acids in these four groups tended to correlate with the variabilities of protein loss from the gastric wall.