Depending on the biomass yield on glucose and the cell morphology of Bacillus thuringiensis, three different metabolic states were observed in continuous culture. At dilution rates between 0.18 h(-1) and 0.31 h(-1) vegetative cells, sporulating bacteria and spores coexisted, while glucose and amino acids were consumed. Only vegetative cells were observed at dilution rates between 0.42 h(-1) and 0.47 h(-1) and glucose was used as the main carbon and energy source. At D = 0.50 h(-1) the biomass yield on glucose decreases sharply. To define better the specific growth rate range in which the microorganism uses mainly glucose, a dilution rate of 0.25-0.35 h(-1) was studied. The experimental data could be adjusted to a Monod model and the following rate coefficients and growth yields were determined : maximum specific growth rate 0.54 h(-1), saturation constant 0.56 mg glucose ml(-1), biomass growth yields 0.43 g cells (g glucose)(-1), and 0.76 g cells (g oxygen)(-1) and maintenance coefficients 0.065 g glucose (g cells)(-1) h(-1) and 0.039 g oxygen (g cells)(-1) h(-1).