The enzymatic defects in a number of Bacillus subtilis mutants of the alpha-ketoglutarate dehydrogenase complex lacking activity have been investigated. Mutants in the citK locus, as well as a series of deletions of unknown length covering the citK locus, are deficient in E1 of the complex, alpha-ketoglutarate dehydrogenase, but have normal activities of E2, dehydrolipoyl transsuccinylase, and E3, lipoamide dehydrogenase. The citK mutants and the citL22 mutant show in vitro complementation of alpha-ketoglutarate dehydrogenase complex activity. The citL22 mutant is severely deficient in lipoamide dehydrogenase activity, and, as a result, lacks activity for both the alpha-ketoglutarate and the pyruvate dehydrogenase complexes. Thus, the E3 components of both complexes are identical. The citL22 mutation maps between ura and metC on the chromosome.