In order to improve the production rate of L-lysine, a mutant of Corynebacterium glutamicum ATCC 21513 was cultivated in complex medium with gluconate and glucose as mixed carbon sources. In a batch culture, this strain was found to consume gluconate and glucose simultaneously. In continuous culture at dilution rates ranging from 0.2 h(-1) to 0.25 h(-1), the specific L-lysine production rate increased to 0.12 g g(-1) h(-1) from 0.1 g g(-1) h(-1), the rate obtained with glucose as the sole carbon source [Lee et al. (1995) Appl Micro biol Biotechnol 43:1019-1027]. It is notable that L-lysine production was observed at higher dilution rates than 0.4 h(-1), which was not observed when glucose was the sole carbon source. The positive effect of gluconate was confirmed in the shift of the carbon source from glucose to gluconate. The metabolic transition, which has been characterized by decreased L-lysine production at the higher glucose uptake rates, was not observed when gluconate was added. These results demonstrate that the utilization of gluconate as a secondary carbon source improves the maximum L-lysine production rate in the threonine-limited continuous culture, probably by relieving the limiting factors in the lysine synthesis rate such as NADPH supply and/or phosphoenolpyruvate availability.