Three different pathways of D,L-diaminopimelate and L-lysine synthesis are known in procaryotes. Determinations of the corresponding enzyme activities in Escherichia coli, Bacillus subtilis, and Bacillus sphaericus verified the fact that in each of these bacteria only one of the possible pathways operates. However, in Corynebacterium glutamicum activities are present which allow in principle the use of the dehydrogenase variant and succinylase variant of lysine synthesis together. Applying gene-directed mutagenesis, various C. glutamicum strains were constructed with interrupted ddh gene. These mutants have an inactive dehydrogenase pathway but are still prototrophic, which is proof that the succinylase pathway of D,L-diaminopimelate synthesis can be utilized. In strains with an increased flow of precursors to D,L-diaminopimelate, however, the inactivation of the dehydrogenase pathway resulted in a reduced formation of lysine, with concomitant accumulation of N-succinyl-diaminopimelate in the cytosol up to a concentration of 25 mM. These data show (i) that both pathways can operate in C. glutamicum for D,L-diaminopimelate and L-lysine synthesis, (ii) that the dehydrogenase pathway is not essential, and (iii) that the dehydrogenase pathway is a prerequisite for handling an increased flow of metabolites to D,L-diaminopimelate.