Ethanolamine ammonia-lyase is a bacterial enzyme that catalyzes the adenosylcobalamin-dependent conversion of certain vicinal amino alcohols to oxo compounds and ammonia. Studies of ethanolamine ammonia-lyase from Clostridium sp. and Escherichia coli have suggested that the enzyme is a heterodimer composed of subunits of Mr approximately 55,000 and 35,000. Using a partial Sau3A Salmonella typhimurium library ligated into pBR328 and selecting by complementation of a mutant lacking ethanolamine ammonia-lyase activity, we have cloned the genes for the 2 subunits of the S. typhimurium enzyme. The genes were localized to a 6.5-kilobase fragment of S. typhimurium DNA, from which they could be expressed in E. coli under noninducing conditions. Sequencing of a 2526-base pair portion of this 6.5-kilobase DNA fragment revealed two open reading frames separated by 21 base pairs. The open reading frames encoded proteins of 452 and 286 residues whose derived N-terminal sequences were identical to the N-terminal sequences of the 2 subunits of the E. coli ethanolamine ammonia-lyase, except that residue 16 of the large subunit was asparagine in the E. coli sequence and aspartic acid in the S. typhimurium sequence.