The specific oxygen uptake rate (q(O2), respiration rate) of Bacillus thuringiensis subsp. kurstaki HD-1 was very high at inoculation and was found to decrease essentially monotonically throughout both vegetative growth phase and transition phase under different batch culture conditions. Average q(O2) values decreased from 8-10 mmol/g h at 1 h after inoculation to less than 2 mmol/g h by the time growth ended. The results are shown to be consistent with the few previous reports on q(O2) in B. thuringiensis in the literature but also novel in that this pattern of monotonic decline has not been described previously. Both pH control and EDTA in low concentration shortened the vegetative growth phase and reduced the 10 h biomass concentration. Using plots of q(O2) versus specific growth rate, mu, biomass yield based on the oxygen used for growth, Y-O2(max) was calculated for transition phase to be 0.041-0.047 g/mmol, consistent with literature values. The same plot also showed that the presence of EDTA resulted in an atypical q(O2)-mu trajectory and apparently much higher biomass yield from the oxygen consumed.