Nitrosation reactions of alpha-, beta-, and gamma -amino acids whose reaction products can act as alkylating agents of DNA were investigated. To approach in vivo conditions for the two-step mechanism (nitrosation and alkylation), nitrosation reactions were carried out in aqueous acid conditions (mimicking the conditions of the stomach lumen) while the alkylating potential of the nitrosation products was investigated at neutral pH, as in the stomach lining cells into which such products can diffuse. These conclusions were drawn: (i) The alkylating species resulting from the nitrosation of amino acids with an -NH2 group are the corresponding lactones, (ii) the sequence of alkylating power is: alpha -lactones > beta -lactones > gamma -lactones, coming respectively from the nitrosation of alpha-, beta-, and gamma -amino acids; and (iii) the results obtained may be useful in predicting the mutagenic effectiveness of the nitrosation products of amino acids.