The mutagenicity of a non-carcinogenic nitrosamine, N,N-dibenzylnitrosamine (I), and a chemically synthesized alpha-acetoxy derivative, N-(alpha-acetoxy-benzyl)-N-benzylnitrosamine (II), has been examined in Salmonella typhimurium TA100 and TA1535. Compound (I) was non-mutagenic when tested directly or in the presence of a metabolic activation system while (II) was highly mutagenic when tested directly. This is the first report on the conversion of a non-mutagenic N-nitrosamine to a mutagen by the formation of an alpha-acetoxy derivative.