Résumé : [en] This paper reports investigations carried out to determine the optimum culture conditions forthe production of hydrogen with a recently isolated strain Clostridium butyricum CWBI1009.The production rates and yields were investigated at 30 ^circC in a 2.3 l bioreactor operated inbatch and sequenced-batch mode using glucose and starch as substrates. In order to study theprecise effect of a stable pH on hydrogen production, and the metabolite pathway involved,cultures were conducted with pH controlled at different levels ranging from 4.7 to 7.3(maximum range of 0.15 pH unit around the pH level). For glucose the maximum yield (1.7mol H2 mol-1 glucose) was measured when the pH was maintained at 5.2. The acetate andbutyrate yields were 0.35 mol acetate mol-1 glucose and 0.6 mol butyrate mol-1 glucose. Forstarch a maximum yield of 2.0 mol H2 mol-1 hexose, and a maximum production rate of 15mol H2 mol-1 hexose h-1 were obtained at pH 5.6 when the acetate and butyrate yields were0.47 mol acetate mol-1 hexose and 0.67 mol butyrate mol-1 hexose.