The mutagenic activity of glycine upon nitrosation was studied in the Ames tester strains TA98, TA100, TA102, and TA104. The results obtained show that glycine at acidic pH values and in the presence of Cl- can react with nitrite giving rise to genotoxic compounds to the tester strains used. When these experiments were carried out in the presence of gastric juice the genotoxicity observed was associated with the Cl- concentration in the different gastric juice samples. The nature and the mechanism of genetic lesion induced by the ultimate genotoxicant arising from the nitrosation of glycine are not fully understood. Primary amines (e.g., amino acids) have been described as potential alkylating agents after nitrosation. However, in our experimental conditions these alkylating activities were not detected, suggesting that other mechanisms could be involved in the genetic lesion induced by nitrosated glycine. The influence of Cl- in the genotoxic activity of glycine and other primary amines upon nitrosation and its possible involvement in the etiology of gastric cancer are discussed.