The apparent effects of operational variables, aeration, agitation, dissolved oxygen, and dilution rate on the L-lysine fermentation by Corynebacterium lactofermentum (ATCC 21799) were investigated in a continuous culture. The results of the present study show that L-lysine production strongly depends on the dissolved oxygen (DO) level and it may become limited at values below 30% saturation. It was also shown that the specific rates of growth, substrate consumption,;product formation and oxygen uptake depend on the dissolved oxygen. Therefore, the oxygen transfer effect should be incorporated in a deterministic model. (C) 2003 Elsevier Science Ltd. All rights reserved.