The concentrations of free D- and L-amino acids were determined in the gastric 
juice from four groups: patients suffering from early gastric carcinoma with or 
without Helicobacter pylori infection, and patients without carcinoma but with 
peptic ulcers, duodenal ulcers or chronic gastritis with or without H. pylori 
infection. H. pylori is a bacterium associated with gastric inflammation and 
peptic ulcers and is a risk factor for stomach cancer. The highest D-amino acid 
ratios (free D-amino acid concentration to the total corresponding free D- and 
L-amino acid concentration) were 29%, 26%, 18%, 4% and 1% for proline, alanine, 
serine, aspartate and glutamate, respectively. The gastric juice levels of 
L-alanine, L-serine, L-proline, L-glutamate and D-alanine in the samples 
obtained from subjects bearing early gastric carcinoma and H. pylori were 
significantly higher than in the samples from the other three groups. Except for 
D-alanine, there was no correlation between the D-amino acid concentrations and 
presence of carcinoma or H. pylori.