The effect of aeration rate on dissolved oxygen concentration in broth, C-DO,C-obs, and specific oxygen consumption rate, Q, was examined in industrial-scale culture of an alkaline cellulase-producing bacterium. In the two stage culture with fructose addition at a specific aeration velocity, SV=0.0075 s(-1), C-DO,C-obs was kept above 2.1 g/m(3) throughout the culture period and a fall in the Q value was moderated in the late stage of the culture. Moreover, DNA concentration in broth measured at the end of the two stage culture was comparable to that from the conventional batch culture at SV = 0.006 s(-1), indicating that cell lysis was suppresed in the two stage culture.