<jats:p> Several diaminopimelic acid (DAP)- and lysine-requiring mutants of <jats:italic>Escherichia coli</jats:italic> were isolated and studied by genetic, physiological, and biochemical means. The genes concerned with DAP-lysine synthesis map at several different sites on the <jats:italic>E. coli</jats:italic> chromosome and, therefore, do not constitute a single operon. Three separate loci affecting DAP synthesis are located in the 0 to 2.5 min region of the genetic map. The order of the loci in this region is <jats:italic>thr-dapB-pyrA-ara-leu-pan-dapC-tonA-dapD</jats:italic> . Two additional DAP genes map in the region between min 47 and 48, with the gene order being <jats:italic>gua-dapA-dapE-ctr</jats:italic> . The <jats:italic>lys</jats:italic> locus at min 55 determines the synthesis of the enzyme DAP decarboxylase, which catalyzes the conversion of DAP into lysine. The order of the genes in this region is <jats:italic>serA-lysA-thyA</jats:italic> .