An assessment of the growth kinetics of acidogenic cells of Clostridium acetobutylicum DSM 792 is reported in the paper. Tests were carried out in a continuous stirred tank reactor under controlled conditions adopting a complex medium supplemented with lactose as carbon source to mimic cheese whey. The effects of acids (acetic and butyric), solvents (acetone, ethanol and butanol) and pH on the growth rate of acidogenic cells were assessed. The conversion process was characterized under steady-state conditions in terms of concentration of lactose, cells, acids, total organic carbon and pH. The growth kinetics was expressed by means of a multiple product inhibition and interacting model including a novel formulation to account for the role of pH. The model has the potential to predict microorganism growth rate under a broad interval of operating conditions, even those typical of solvents production. (C) 2010 Elsevier Ltd. All rights reserved.