This paper investigates the influence of pH and temperature on hydrogen bioproduction by Enterobacter aerogenes (NCIMB 10102) utilizing starch hydrolysate as substrate. An optimum pH range corresponding to 6.1-6.6 is the main evidence of batch runs carried out at different pl-Is. An optimum value of temperature corresponding to 40 degreesC is experimentally determined by means of batch fermentation runs carried out at different operative temperatures. A thermodynamic study, which was performed developing the Arrhenius approach, allows the estimation, for both fermentation and thermal inactivation, of the activation enthalpics (67.3 and 118.1 kJ mol(-1)) and of the correlated entropies (-0.087 and -0.46 kJ mol(-1) K-1).