B. amyloliquefaciens fmb50 in the bioreactor reached up to109CFU/ml after 15 ± 0.2 h culture, and then the cell growth went into stationary phase (Fig. 1A). However, in control 3,cell growth declined from 12 h of cultivation. That may be due to the agitation rate changing between 150 and 250 rpm;normal cell growth seemed to be inhibited and the biomass decreased due to the simultaneous increase of the overflow. B.amyloliquefaciens fmb50 reached its maximum specific cell growth rate at 6 h of cultivation in control 1, which was 4 h earlier than in control 2 (Fig. 1B). In control 3, where cell growth was disturbed, a lower specific cell growth rate was observed. The maximum specific cell growth rate was low-ered nearly by half with respect to controls 1 and 2. Although the increase in the agitation rate promoted quadratic cell growth, this one was not delayed.Surfactin production is essentially associated with cell growth 7,16, although high biomass does not necessarily meanhigh surfactin production. It seems that a lower specific growth rate is more conducive to the production of biosur-factants such as mycosubtilin4. The effect of agitation andaeration rates on cell growth and cell specific growth ratewas studied in this paper and the best control strategy waschosen to enhance surfactin production.