The requirement for succinate in a thiamine-1ess mutant strain of E. coli, 70-23,was substituted by both lysine and methionine, although there was a considerable lag before growth occurred with these substances. About one tenth as much amount of thiamine was formed in the mutant cells grown anaerobically with succinate as compared with the wild-type cells grown under the same conditions. This might account for the fact that suspensions of the organism grown on succinate oxidized pyruvate very slowly but did so quickly upon the addition of thiamine. Quantitative studies indicated that succinate-dependent growth was markedly stimulated by thiazole moiety of thiamine. Furthermore, thiazole moiety alone was able to support very slow growth of the mutant under anaerobic conditions, while aerobically the growth did not occur even in the presence of pyrimidine moiety. It was already pointed out that a large amount of pyrimidine was accumulated in the culture when the organism was grown with a limited amount of thiamine. Therefore, it followed that in the mutant strain thiamine might not be formed until the considerable accumulation of intracellular metabolites including succinate, pyrimidine and thiazole moieties had occurred. (Received October 26,1970)